A few days ago I got stuck in a project to migrate a set of test cases from an “old” Team Project to another (new) Team Project in another Team Project Collection (TFS 2013 Update 4 environment). Via the TFS API I used the work item Copy method to perform a deep copy [including links/attachments] with the WorkItemCopyFlags set to CopyFiles.
This always worked when copying test cases to a Team Project in the same Team Project Collection (TPC) as the original Team Project, but copying the test cases to a Team Project in another TPC always caused an error:
TF237136: File attachment was not found on attachment server.
I expected this to work, but after I verified that the MTMCopyTool also generated the same error when copying test cases across Team Projects, I decided to search for a workaround … downloading and uploading the attachments as after-processing.
Not perfect, but good enough to keep going and moving all attachments to the other Team Project in the other Team Project Collection.