This is a bug that was introduced in Unity late in the Unity 5.3 cycle which I believe is related to a change Unity made related to objects which as sub assets like Unity's fonts and TMP's Font Assets.

For whatever reason, when saving a scene or creating a build, Unity appears to lose track (internally) to the material or texture used by the font asset which both happen to be sub assets.

When this issue occurs while saving a scene, it isn't too much of an issue as entering play mode or changing the properties of the text object will make the text reappear.

However, when it comes to creating a build, this can lead to the issue reported here and corruption of the font asset.

Until Unity fixes this issue, you can enable "Verify Saving Assets" in the Unity Preferences. With this feature enabled, when creating a build or saving a scene, Unity will prompt you to accept or decline saving assets. So when creating a build where the font assets or materials should not be modified (saved over by Unity which leads to this corruption) simply decline saving over those assets.

I did make a change in release 1.0.55 of TextMesh Pro which will be available over the weekend which should stop Unity from trying to save the font asset or material when it hasn't been changed. This change should greatly reduce the potential of this issue happening but the underlying bug in Unity will remain until this is fixed.

I was just made aware today of this bug report hence why I am just now providing this additional information. I will once again reach out to Unity to inquire about a time frame for a resolution to this issue.

I just solved the problem :
1) Delete the TextMeshPro folder from your Asset folder
2) Open project
3) Reimport TextMeshPro

We're having what appears to be the same or similar problem; unable to open our project as Unity will crash while loading Assets. We've tried clearing Library & Temp, usually that's worked in the past, does not appear to be working this time. :-(

I have the same problem in Unity 5.3.5f1.
Did not really change anything. Yesterday everything was working and today I can't open my project anymore.

What can I do?

This is an issue with TextMeshPro. I edited a material and my project froze. Re-opening would lead to an immediate freeze. Rebuilding the library tossed an error that it couldn't find sharedassets0.assets.resS, which led me to this thread.

Seeing so many other people have the problem made me sure that it was with TMPro. I had to delete the offending material. that was all. Now I'm back up in action.

Still happening in Unity 5.4.3f1. It happened after changing editor settings to force asset serialisation to text (was mixed). The editor crashed and the project would not reopen again. The project uses TextMeshPro and the crash happens when importing 'TMP Settings.asset'. Deleting the library and reopening the project to force a reimport does not help - it still crashes at the same place.

Editor log: Cancelling DisplayDialog because it was run from a thread that is not the main thread: Opening file failed Opening file /myProjectPath/sharedassets0.assets.resS: No such file or directory.

Anyone find a solution for this? I can no longer open my project. Unity 5.4.1f1. I have Dropbox running, like someone else mentioned.

Using Unity 5.4.2f1 I'm still able to reproduce this. From what I can see it only happens if one edits text properties of TextMeshPro (TMP) text (eg. outline, colour, texture, etc.) then does a build. If after the changes to TMP text I save my scene and project and do the build I don't see the crash, if I make the changes and DON'T save scene&project and then proceed to do the build the crash occurs. Then it's necessary to remove the asset font file to get the project to load. This is on a Mac by the way. If anyone can confirm the same behaviour, please let us know.

Also having this issue with multi-object assets getting corrupt after builds. Saving the scene also seems to do unneeded changes to the asset (it gets checked out from version control), but it seems to only crash/freeze after builds (standalone Windows in my case). The asset in question is a TextMesh Pro font asset file.

I had this issue twice today with Unity 5.4.2f1
It always happens when I work in Monodevelop, Unity decides to update assets that haven't changed and freezes with this problem. The file you find in the editor log is then corrupted and will cause a crash if you try to access it. If the file is removed/replaced everything is back to normal again.