Error MSB6006: “mt.exe” exited with code 31

Question

I ran into this problem today while migrating a VS2008 solution to VS2010. The problem occurred in either of the following scenarios:

1. Rebuild Solution

Answer 1

Giving credit to https://social.msdn.microsoft.com/Forums/windowsdesktop/en-US/c5a3e2c3-fbf4-4268-a551-8cee195be586/test-case-13-for-vista-certification?forum=windowscompatibility, I found this was resolved by fixing the '-' character in the post build commandline. I believe some bad copy/paste efforts have replaced a hyphen with a dash.

Answer 2

In my case it was a problem with TortoiseGit. Removing Debug and Release folders from the GIT repository solved the problem.

Answer 3

Using process monitor and dbgview I discovered msmpeng (Microsoft Security Essentials) was accessing the file, just when mt.exe wanted to have it exclusively. Excluding the development directory solved the problem. It is still a workaround of course.

Answer 4

deleting the "program debug database" in "debug" folder worked for me.

This problem happened when I was running the .exe in the debug folder on high priority.

Answer 5

WARNING: This exact error can also happen as a result of having a Windows Explorer window open in the folder containing the *.exe which you are currently attempting to build.

For example: Explorer open in /.../MyProj/Debug/ while trying to build the Debug version of your code in Visual Studio.

I was angry with myself for ~10min before realizing this.

Answer 6

Try turning off Windows Defender (or possibly other anti-virus related software). Windows Defender is known to lock files because MT.EXE runs after the linker is finished. WD jumps in the middle to check up on the newly built EXE and locks it up for the MT.EXE.