I am currently working with a Perforce repository that has been configured with a 'Root Directory' specified as '2015/Main'. Any time that repository is synced on a clean host (a newly provisioned one, or one that's had it's workspace deleted using the QuickBuild interface), if fails with a message similar to the following:

[* ]Step '<step>' is failed: Cannot run program "sh" (in directory "<workspace>/2015/Main"): error=2, No such file or directory

It seems as though QuickBuild is attempting to run a shell script to perform the sync before the workspace directory even exists, so a potential fix for this issue would be to ensure the finalized workspace root directory is created before attempting to run the script.