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Fixed in 5.6.0



Found in


Issue ID




UnityEngine.UI.dll is in timestamps but is not known in guidmapper...

Error message shown on first open of attached project:

Asset 'C:/Program Files (x86)/Unity/Editor/Data/UnityExtensions/Unity/GUISystem/4.6.0/UnityEngine.UI.dll' is in timestamps but is not known in guidmapper...

Comments (85)

  1. mark_madatom

    May 13, 2015 17:09

    Can confirm this bug is still present in 5.0.1p4.

  2. findujanvier

    May 12, 2015 01:38

    It also happens on 4.6.4f.
    Delete library folder and restart editor can solve the problem.
    It is still annoying!

  3. GameEnggineer

    May 09, 2015 05:53

    It Occured in Unity 5.0.1f1 personal edition.

  4. k0mbain

    May 08, 2015 07:06

    @DBURDEN1: I agree, after few restores from backup there is a need to reimport whole library from scratch, because restoring does not give effects. But in a short term it is some temporary solution.

  5. dburden1

    May 07, 2015 15:13

    In my experience, making backups of the Library folder is not worth any time it might save you--if it saves any at all. It seems like when Unity detects any unexpected change with the Library folder, it wants to re-import the entire project, effectively "deleting" the Library folder itself.

  6. k0mbain

    May 07, 2015 09:23

    We have a huge project too and reimporting library is taking about 4 hours too. It can happen even every day! Part of our team had to switch back to Unity 4.
    The workaround may be making a backups of whole Library folder as often as possible. When the error occurs just remove broken Library and replace with backuped - it will reimport some new assets but Project will be working for some time. But... its f*** annoying copying folders all the time.
    The problem occurs not only when you change asset's name. It occurs when you are modifying project from outside Unity too, i.e. when source control system is used.

    Unity Devs, this issue should have highest Priority and Severity and should be fixed immediately! A lot of people is wasting their time and money because of this bug. It prevents of using Unity at all...

  7. jyves69

    May 07, 2015 08:47

    We are 15 developpers and it appends randomly 2,3 times per week. Each time it's about 4 hours lost !!

  8. jposey

    May 06, 2015 21:12

    Does anyone have a better "workaround" for this than deleting and reimporting the entire Library whenever files are renamed or moved? Are there more specifics to watch out for such as the "Occurs when you change any char in the asset's name from lowercase to uppercase."? We have been doing some project cleanup and everyone is losing a ton of time reimporting Library every day. Thanks!

  9. dburden1

    May 06, 2015 21:02

    Every time this happens, it causes us to lose hours of that day, because we have to delete our libraries and wait for them to reimport in order to run our game. We have a very large project, and it takes a very long time to reimport everything. Please, please, fix this.

  10. stoneedge

    May 06, 2015 03:51

    Getting this in 5.0.1 OSX. Let me know if you need a test case.

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