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Fixed in 2018.3

Fixed in 5.5, 5.6, 2017.1, 2017.2, 2018.1, 2018.2



Found in



Issue ID




Unity throws out Fatal Error: Callback registration failed kMaxCallback



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.

  1. 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 (207)

  1. 0afd0bfcedf6b9f4509f05f71e45df7d?d=mm


    Aug 31, 2018 22:30

    Still the case for me too....

  2. 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)

  3. Abcf84d9d9261efed6f6cfe09c7e7b3a?d=mm


    Aug 29, 2018 19:47

    it's still happening regularly on 2018.2.0f2

  4. 8b3646f8bc6a52cf1ef96345133f511b?d=mm


    Aug 29, 2018 00:39

    Still happening on a build with Unity 2018.2.5 - NOT fixed

  5. C5e4ece353abd7a622140c827974298e?d=mm


    Aug 26, 2018 14:38

    Still not fixed

  6. 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.

  7. Db0fd1fe3e248395c4daa6225920e576?d=mm


    Aug 23, 2018 05:40

    Happened today to me 5 times .-. v2019.2.3f1

  8. A3a43487ce4126a5c71e6126f32d5e71?d=mm


    Aug 22, 2018 21:26

    (1056461) - Editor: Fixed case of "Callback registration failed kMaxCallback" error.

    Feel free to test.

  9. 2431b57af79a922a64fa177910803e54?d=mm


    Aug 22, 2018 09:25

    Happens at least once a day, in latest versions of Unity, its been like a month, hope this gets resolved soon.

  10. 7f03b8af39750f36c17006c58ea51351?d=mm


    Aug 21, 2018 22:42

    This is not resolved. Please make a new listing. I'm having this issue in 2018.2.3f1.
    The last time it happened I had just saved in the last 10 seconds. Is there a relationship to actually saving?

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