TFS Error - There is not enough space on the disk

I've been working on trying to automate our development workflow or in other words I've been banging my head against the TFS wall trying to set up CI.

I thought i had everything working when I encountered this little beauty for one of the ASP.NET projects:

The build server had over 20 GB of free space, so I was somewhat baffled by this error message, so I did what every self respecting IT professional does: I started bouncing stuff.

After I bounced, the build agent, build service and the server itself, all to no avail, I hit the interwebs where I found the solution.

This error has got nothing to do with disk space, it's related to tempory files not being deleted in this folder:

C:\Windows\Microsoft.net\Framework64\<version>\Temporary ASP.NET Files

I checked the folder and sure enough there was a subfolder with the name of one of the projects. I deleted this and the builds started to complete again.