Search Issue Tracker

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. B73bcdee47ea96e48ea9fe349cc61ada?d=mm


    Aug 26, 2017 23:20

    A dozen crashes a day with this error on MacOS with latest version of Unity. Praying for a fix.

  2. 2ecf0c3c4065a1a1fbf18f32275190fe?d=mm


    Aug 25, 2017 08:58

    this is happening to me now around 5 times per day! Very frustrating. Lost some work a few times now.


  3. A426725f19002fd2bbb88ed2d43d1a9e?d=mm


    Aug 23, 2017 10:25

    Most annoying bug! I almost destroyed my keyboard because of that ;) ... Still happening on Unity 2017.1.0p4(p3)

  4. B89ae67e47d974f5a427480148083a89?d=mm


    Aug 20, 2017 18:51

    Ouch, save often and always before play mode! My scripts were not erased, but my editor creations were. Sadness is overwhelming. =P

  5. Dbd49e53586c7ee10350caa4e5220f76?d=mm


    Aug 20, 2017 13:22

    Please, please release an urgent fix for this bug! I get this up to 10 times a day working on projects! Occurs mostly switching between monoDevelop and Unity Editor often during debug sessions.

  6. 6eaec9c6f56d1517958733fac1fabde3?d=mm


    Aug 19, 2017 20:46

    Zeday, this issue doesn't affect scripts. It affects the editor, not monodevelop or your other scripting programs, so just don't close out of your other programs. I hope this helps you moving forward if you ever experience this issue again.

  7. Dc1b254760f44d16cd4f684456bf554f?d=mm


    Aug 18, 2017 15:24

    A possible fix is on the way.
    Please direct feedback to this thread:

  8. Aff8fc7166d982bd670e1d90aab016ed?d=mm


    Aug 18, 2017 04:24

    I'm new to Unity so I thought that maybe this was a known issue with a workaround. I'm pleased to see that I'm not the only one with this issue but very annoyed like everyone else at the amount of work I've lost.

    Same thing for me: Occurs randomly after about 30 minutes to an hour. I've found that sometimes my work reverts to a state before my most recent save of the project which forces me to pray every time I reopen after a crash that my work didn't revert too far.

    Working with a MacBook Pro.

  9. E68f3fd980fe292e9ee28caebfc35969?d=mm


    Aug 17, 2017 02:05

    009, I started experiencing this error almost immediately upon installing 2017.1.0f3. I did not enable the Collaboration service and had it occur several times. So far, the "using Visual Studio as script editor and hitting the Play button" seems to be the most likely trigger in my case. But since it doesn't always happen right at the instance that I hit play or quit play, I can't be certain.

  10. 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.

Add comment

Log in to post comment

All about bugs

View bugs we have successfully reproduced, and vote for the bugs you want to see fixed most urgently.