tfsbuild - Really strange error at the very end of a TFS 2015 build -

i'm trying convert xaml builds tfs 2015 builds , running problem build seems complete trows following error:

and in case can't see image, error is:

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finishing task: vsbuild

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system.notsupportedexception: given path's format not supported. @ system.security.permissions.fileiopermission.quickdemand(fileiopermissionaccess access, string fullpath, boolean checkforduplicates, boolean needfullpath) @ microsoft.teamfoundation.distributedtask.agent.common.contextextensions.getexpandedpath(ilogservicecontext context, string path, string defaultpathroot) @ microsoft.teamfoundation.distributedtask.worker.jobrunner.resolveinputs(ijobcontext context, ijobextension jobextension, taskwrapper task, idictionary`2 variables) @ microsoft.teamfoundation.distributedtask.worker.jobrunner.run(ijobcontext jobcontext, ijobrequest job, ijobextension jobextension, cancellationtokensource tokensource) worker worker-44f37a2f-ff1b-43a7-b619-88373a8687c0 finished running job 44f37a2f-ff1b-43a7-b619-88373a8687c0

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finishing build

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it doesn't give me clues code that's causing error don't know look. when in c:\agent_work\5\a folder looks project building fine (although have no way of verifying that). of files seem there including subdirectory created .exe called in post-build event on last .csproj file in solution never expected called , run in tfs 2015! knew - that's great! if build start working...

i figured out. trailing backslash on source folder. had $(build.artifactstagingdirectory)_publishedwebsites\botwsitecoreweb\ when should have been $(build.artifactstagingdirectory)_publishedwebsites\botwsitecoreweb. happened guess - there no logs.