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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 (205)

  1. Dc1b254760f44d16cd4f684456bf554f?d=mm


    Sep 20, 2017 11:30

    2017.1p1, not 2017.1f1.
    The p stands for patch and can be found here:

  2. 4c1d9ac922b834a76e3d157ca9d332ae?d=mm


    Sep 20, 2017 04:59

    If this is fixed in 2017.1.1p1 why is it not being pushed to the public?? I just lost my entire project to this and I'm running the latest non-beta release 2017.1.1f1 according to the Unity updater and the latest installer.

  3. 0c08b6a68d2f51913b5acf86bd11f38e?d=mm


    Sep 19, 2017 03:07

    Same problem in version 2017.1.1f1... My PC is not a NASA computer so I must wait 2 ~ 3 min to reopen my projects every time this bug happens...
    Windows 7 Professional 64bits SP1

  4. 1f2899aa5fc8c30aa97a7ffcc1be6cfe?d=mm


    Sep 18, 2017 22:19

    Lol, what are you talking about? This issue isn't fixed and I'm using version 2017.1.0f3. In fact, this time around it actually corrupted my project where now the project won't even load causing a crash each time.

    Oh, I do want to say, though, that I appreciate all of the hard word you put into fixing these issues and I know I sound a bit snarky, lol. :)

  5. 81c9cca8ee0e136fe3c626fc762cb689?d=mm


    Sep 18, 2017 12:13

    The same here
    System: Windows 10 Pro 64 bit
    Unity : 2017.1.1f1 64 bit
    it's very annoying - every ~30 minutes.

  6. 2b75553ec4875ac66bc78f8f38415a74?d=mm


    Sep 17, 2017 19:31

    Same problem in version 2017.1.1f1 education version on Windows 10 x64. Running the update tool from the help menu says this is the most current version.

  7. F1f287055d4c271281828ef18b550638?d=mm


    Sep 16, 2017 19:54

    The issue remains in 2017.1.1f1

  8. Dc1b254760f44d16cd4f684456bf554f?d=mm


    Sep 13, 2017 11:35

    If you still have this issue in 2017.1.1p1 then please file a bug report and/or post here with your log file

  9. 690dd33162f4b442491b979ebed4d53e?d=mm


    Sep 12, 2017 11:53

    Still an issue on 2017.1.1f1

  10. B67ce856fdd72199c8b8ded4754496f2?d=mm


    Sep 12, 2017 11:21

    At least do the auto save on forced exit!

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