This error message is not one of git-tfs, but one of TFS (I just looked at the source code).
, git-tfs shelveset, , git-tfs, . - , :( , !
, , , , "". , , (, , , , ), !
, , git commit .
shelveset unhelve! , (, git , ).
, ...
TFS :(
edit: , , git-tfs , , .
edit2: , --force