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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. karl_jones

    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. zero_null

    Aug 02, 2018 15:26

    happening to me as well. Just like GIAWA said, it randomly crashes when coming back from editing scripts in the visual studio most of the time.

  2. Khitty

    Aug 01, 2018 22:04

    This just happened to me. Glad I'm not the only one. I was using the Serial Port class to get info from my Arduino. Hit play and the editor just closed. Had to look in the Editor-prev.log to figure out what happened. And I only did that because my callback function is no longer being called after restarting the editor =(

  3. mnwarren

    Jul 30, 2018 10:28

    Unity 2018.2.1f1 on Windows 10 x64 just crashed with the error reported in this issue.

  4. giawa

    Jul 27, 2018 23:08

    Happens to me in 2018.2.0f2 (Windows), usually when recompiling scripts after editing in Visual Studio. Using latest Unity extensions for Visual Studio.

  5. AlfieBooth

    Jul 27, 2018 13:02

    This happens to me too.
    Specifically, it happens more when I have two or more Inspector tabs on the go... and it will certainly happen if I hit play with both tabs open.

    Hope this helps.

  6. hippocoder

    Jul 26, 2018 21:09

    Still happening happily disrupting my work in 2018.2.1 LTS

  7. ehabroshdy

    Jul 25, 2018 04:23

    it occurs usually when pressing Play
    Version 2018.2.0f2.

  8. Psyboyo

    Jul 24, 2018 13:58

    Happens frequently on 2018.2.0f2 (Windows)

  9. xmastree

    Jul 21, 2018 09:46

    On 2018.2.0f2 (Windows) happens regulary

  10. JohnnyFactor

    Jul 21, 2018 01:15

    I have gotten this error six (6) times since July 11, 2018. Always when pressing Play. Version 2018.2.0f2.

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