Common .ics File Errors and How to Fix Them

(Google Calendar, Outlook, Apple Calendar, iCloud, Teams, Office 365)

If you’re trying to import an .ics file into Google Calendar, Outlook, Apple Calendar, or a custom app — and it won’t load — you’re not alone.
ICS files follow the iCalendar specification, but real-world exports are often invalid, incomplete, or malformed.

This guide explains:

The most common ICS errors
Why Google/Outlook/iCloud reject certain files
Examples of broken vs corrected ICS snippets
How to validate or autofix issues programmatically
When to use a tool like CorrectICS to clean the file

This page is optimized for engineers, QA teams, and operators who deal with ICS imports/exports from CRMs, booking systems, and legacy tools.

1. “This event cannot be saved” / “Unable to import file”

This is the #1 ICS failure across Google Calendar, Outlook, and Apple Calendar.

Cause

The ICS is missing one of the required VCALENDAR or VEVENT boundaries:

BEGIN:VCALENDAR
END:VCALENDAR
BEGIN:VEVENT
END:VEVENT

Broken Example

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BEGIN:VCALENDAR VERSION:2.0 BEGIN:VEVENT DTSTART:20250310T090000Z SUMMARY:Team Meeting

Corrected Example

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BEGIN:VCALENDAR VERSION:2.0 BEGIN:VEVENT DTSTART:20250310T090000Z SUMMARY:Team Meeting END:VEVENT END:VCALENDAR

Fix

Ensure all component blocks are properly closed.

Automatic fix: upload file to CorrectICS
Programmatic fix: use the CorrectICS API (see section 9).

2. Missing or invalid DTSTART/DTEND

Most calendar clients require:

DTSTART (start time)
DTEND or DURATION

Broken Example

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BEGIN:VEVENT SUMMARY:Lunch DTEND:20250310T130000Z END:VEVENT

Corrected Example

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BEGIN:VEVENT DTSTART:20250310T120000Z DTEND:20250310T130000Z SUMMARY:Lunch END:VEVENT

Google Calendar is especially strict here — if DTSTART is missing, the file fails silently.

3. Invalid or unsupported TIME ZONES (TZID issues)

This is one of the most subtle ICS problems.
Common errors:

TZID=EST (not valid — needs Olson format)
TZID=GMT-5 (nonstandard)
Missing VTIMEZONE block
TZID mismatch between DTSTART and VTIMEZONE

Broken Example

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DTSTART;TZID=EST:20250310T090000

Google and Apple Calendar do not accept EST as a valid TZID.

Corrected Example

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DTSTART;TZID=America/New_York:20250310T090000

If the VTIMEZONE block is missing

Some clients (Outlook desktop) require it for floating times.

Automatic fix

CorrectICS automatically:

normalizes TZIDs
adds missing VTIMEZONE blocks
resolves ambiguous time zones

4. RRULE / Recurrence errors

Recurring events are the most frequent source of ICS failures.

Common issues:

Missing FREQ=
Invalid BYDAY or BYMONTH
Unsupported rules (Outlook Web is stricter than Apple/Google)
Infinite recurrences with no UNTIL or COUNT (some clients reject)

Broken Example

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RRULE:BYDAY=MO,WE,FR

Corrected Example

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RRULE:FREQ=WEEKLY;BYDAY=MO,WE,FR

Broken Example 2 (invalid UNTIL date)

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RRULE:FREQ=DAILY;UNTIL=20250230T000000Z

Corrected

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RRULE:FREQ=DAILY;UNTIL=20250228T000000Z

CorrectICS validates and normalizes recurrence rules so they work in all major clients.

5. Duplicate or missing UID (required by the spec)

Every event must have a globally unique UID.

If you generate ICS files programmatically (from CRMs, custom apps, CSV imports), you may forget to include one.

Broken Example

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BEGIN:VEVENT DTSTART:20250310T090000Z SUMMARY:Meeting END:VEVENT

Corrected Example

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BEGIN:VEVENT UID:20250310T090000Z-1234@example.com DTSTART:20250310T090000Z SUMMARY:Meeting END:VEVENT

CorrectICS auto-generates stable UIDs if missing.

6. Missing VERSION or PRODID

Some calendar apps silently reject ICS files missing:

VERSION:2.0
PRODID:-//YourApp//EN

These fields seem harmless, but older Outlook and Apple Calendar builds treat them as required.

Broken Example

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BEGIN:VCALENDAR BEGIN:VEVENT ...

Corrected Example

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BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CalendarExporter 1.0//EN

CorrectICS adds these if missing.

7. CRLF vs LF line endings (Windows vs Unix)

ICS files should use CRLF (\r\n).
Many exporters use just LF (\n), which breaks:

older Outlook
some Exchange servers
certain enterprise calendar sync tools

CorrectICS normalizes line endings automatically.

8. Long lines / folded lines incorrectly formatted

ICS uses a line-folding mechanism:

Lines >75 bytes must be folded
Continuation lines must begin with a space

Broken Example

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DESCRIPTION:This is a very long line that goes over the recommended length which will cause some ICS consumers to reject the file outright or silently fail to parse it

Corrected Example

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DESCRIPTION:This is a very long line that goes over the recommended length that will be folded correctly.

This is annoying to do manually — CorrectICS handles it for you.

9. How to validate & autofix ICS programmatically

Developers often prefer API workflows instead of manual uploads.

Validation

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curl -X POST https://api.correctics.com/v1/validate \ -H "Content-Type: text/calendar" \ --data-binary @broken.ics

Autofix

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curl -X POST https://api.correctics.com/v1/autofix \ -H "Content-Type: text/calendar" \ --data-binary @broken.ics \ -o fixed.ics

Typical uses:

nightly CI checks on calendar exports
ingesting ICS feeds from vendors
verifying ICS generated from CSV → ICS pipelines
sanity checking user-uploaded calendar files in a SaaS app

10. When you should NOT manually repair ICS files

If:

you’re a SaaS app supporting many users,
you import ICS from multiple vendors,
you export ICS for other systems, or
you deal with recurring time zone issues,

…then manually fixing files is not sustainable.

Use:

CorrectICS for one-off fixes
CorrectICS API for automation

Your total time spent on ICS goes from hours to ~5 seconds.

11. Conclusion: ICS files break for predictable reasons

Most ICS failures boil down to:

missing structural boundaries
missing DTSTART/DTEND
invalid time zones
malformed RRULEs
missing VERSION/PRODID/UID
bad line endings
invalid line folding

If you’re debugging ICS files regularly — or supporting customers who are — the fastest way out is to:

validate with CorrectICS
autofix automatically
integrate the API into your testing or ingestion flow

View pricing