Over the last weekend, our TFS 2013 server decided to stop building projects for no apparent reason.   No one had changed any software on the TFS or build controller servers and the only evidence of a problem was the following message in the “Diagnostics” log file for each build:TFS Error MessageAfter spending hours searching for solutions to this problem and finding nothing, I finally figured-out the cause of the issue.   The primary hard drive on the TFS server (not the build agent) was completely full.   After sending a request to our infrastructure team to add more storage to the primary hard drive on the virtual server that hosts our TFS implementation, the builds started working again.