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Fixed in 2018.3.X

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



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 (202)

  1. 90af5cb444e49113735c00e690af5520?d=mm


    Aug 17, 2017 02:00

    Is it possible that is cause by Unity Collaborate ? Found out the only differences from me and my colleagues is this.

  2. 7acb3a48fc874dd4b32db9a644be779f?d=mm


    Aug 16, 2017 20:06

    Oh, Unity, WHY.....??? Why have you done this to me ...and others apparently??
    I have lost hours of work, hundreds of lines of code.

  3. 2bfd18e078ab086d8dda165caa3882ac?d=mm


    Aug 16, 2017 17:00

    Same problem... annoying as hell. I've lost so much work and finding I have to save every little change I make. Any update on when this will be fixed.

  4. 90af5cb444e49113735c00e690af5520?d=mm


    Aug 16, 2017 08:30

    Occur when after I edit the code with monoDevelope and come back to the Editor. about 5 times within 6 hours of working. Hope this can fixed soon.

    Unity 2017.1.0f3 in Window OS

  5. 04acf4ab7adba6df33a9bebb9e101413?d=mm


    Aug 16, 2017 03:46

    Happening to me since upgrading to 2017.1.0f3 . It's consistent after 30 minutes to an hour of use, it crashes. It usually seems to crash while I'm saving, but that's not always.

    OS: Mac

  6. B6ead0b30a2a3467d2c3b9f9e030c96e?d=mm


    Aug 15, 2017 14:36

    I've been having this issue since switching to 2017.1.0f3.
    It seems to be a random issue and causes alot of wasted time. Is there currently any workaround for it?

  7. F27617e362df1b431c68e2cbc49040bf?d=mm


    Aug 14, 2017 18:23

    Mac, 2017.0.1f3 - Please let me know if I can help repro, I get it several times a day and it's very hurtful to our progress.

  8. 854e499507e78aa82deb1c6a8858435c?d=mm


    Aug 13, 2017 22:11

    God! Please friggin fix it! We are losing progress and need to reset scenes!!!
    The hell?! 2017.1.0p3 and still happening.

  9. 40d9242731643561050862cdb8f66f2b?d=mm


    Aug 13, 2017 17:11

    This is clearly happening to a large group of people and is certainly a hefty annoyance. Can we get some official Unity word on what the plan is for this? If this issue was any more frequent it would be a show stopper.

  10. Ea7a78df7acb9ead19af66d6199a1bbf?d=mm


    Aug 13, 2017 16:19

    Happens always after a period of time (~half an hour) when switching from Visual Studio to Unity and hitting play. I have not experienced error to show up when using JetBrains Rider yet.

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