when i try to unlocking the file 
 
system prompt the message : unable to determine the source control server 
 
 
 
 
 
 
How to resolve the issue:
 
 
 
step 1:
 
add the collection URL follows the command :
 
tf undo /workspace:ABC123;DEF/echo $/TestProject/File/Path/Tempalte.doc /s:"http:10.123.4.5:6060/tfs/defaultcollection"
 
 
 
step2:
 
run the command 
 
 
 
operation completed successfully