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Fixed in Unity 2018.3



Found in


Issue ID




Unity throws out Fatal Error: Callback registration failed kMaxCallback




Priority: 2Necessary for shipping a final release


Severity: 1Crash, freeze, data loss, work stops

Unity throws out Fatal Error: "Callback registration failed kMaxCallback" after working with the project for 30 minutes or more. It appears randomly.

1. Actively use Unity for more than 30 minutes

Actual: Unity continues to work
Result: Unity crashes with Fatal Error.

Reproducible with: 2017.1.4f1, 2017.2.3p1, 2017.4.4f1, 2018.1.3f1, 2018.2.0b6

Reproduced on macOS, Windows, Linux.
Bug Report window does not appear.
Scene files are not restored after reopening Unity so all not saved Scenes are lost.

Response avatar


Jan 04, 2019

Please file a new bug report If you are still encountering this problem. The error message is a symptom and can be caused by many different areas. The area for this bug has been fixed.

Comments (201)

  1. A6fc986ab7f0eaafedad213af21bf52f?d=mm


    Apr 30, 2019 08:22

    Happened to me many times,v2018.2.3f1

  2. F9033d33caeaaf5c0bd043ac4528862b?d=mm


    Apr 23, 2019 01:01

    STILL HAPPENING IN 2018.2.0f2

  3. 762bc915f22a530e1370c07f9ef6eb32?d=mm


    Sep 13, 2018 13:58

    2018.2.7 Not fixed. What to do? Wait for 2018.3?

  4. E554a28755f5d7c27767063338a43547?d=mm


    Sep 02, 2018 18:11

    This is becoming annoying.
    Happens on a daily basis now, and has for a month or so (using 2018.2.x.
    I never encountered it before 2018.2 (or so rarely I never noticed it).

  5. 0afd0bfcedf6b9f4509f05f71e45df7d?d=mm


    Aug 31, 2018 22:30

    Still the case for me too....

  6. 4ff0f9c8dada5a37a1a83e4c97054f73?d=mm


    Aug 30, 2018 05:09

    Related but unrelated. I get this same crash message in the log in windows standalone build when I run the build when built with 2018.2.5f1 but it works fine when built with 2018.2.3f1

    Callback registration failed. Increase kMaxCallback.
    (Filename: Line: 191)

  7. Abcf84d9d9261efed6f6cfe09c7e7b3a?d=mm


    Aug 29, 2018 19:47

    it's still happening regularly on 2018.2.0f2

  8. 8b3646f8bc6a52cf1ef96345133f511b?d=mm


    Aug 29, 2018 00:39

    Still happening on a build with Unity 2018.2.5 - NOT fixed

  9. C5e4ece353abd7a622140c827974298e?d=mm


    Aug 26, 2018 14:38

    Still not fixed

  10. A3a43487ce4126a5c71e6126f32d5e71?d=mm


    Aug 23, 2018 13:13

    Tried the latest 2018.2.5f1 which claims to fix the issue, however unity crashed and quietly closed with no error at all this time. It never did so like this in previous versions so it could be related or simply a bad fix.

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