If you need to revert or rollback to a precedent working revision, do not just try editing a past version. You may be unable to make a commit.

Instead, make a new commit that undoes all of the changes made, from the revision you want to bring back, up to the Head. 

To do this, proceed backwards, step by step, using "Revert Changes from Revision xx" functionality, from the last revision to the revision you want to bring back.


For Example, to rollback to revision 12, sequentially execute:

 - Revert Changes from Revision 17 (your code is now as in revision 16),

 - Revert Changes from Revision 16 (your code is now as in revision 15),

 - Revert Changes from Revision 15 (your code is now as in revision 14),

 - Revert Changes from Revision 14 (your code is now as in revision 13), 

 - Revert Changes from Revision 13 (your code is now as in revision 12).