When I attempt to save a template, I get an error: Template not saved: Please make sure that you do not have 2 templates with the same alias.

In looking at my templates, I do indeed have two named "test" in the Umbraco UI, but in the file system there is only one. I don't know how this happened or how to fix it. I tried deleting the file from the file system, but that didn't remove either from the UI. Next I tried deleting both "test" entries in the db table cmsTemplate. However, this caused all my template nodes to disappear from the UI tree. I added them back from an older version of the db and that brought the tree nodes back, but of course I am still left with the orginial problem of being unable to edit any templates. I did verify that the app pool has modify persmissons on the folder, exactly the same as the other folders. 

EDIT: Here's another piece of the puzzle. I can create a new template in the UI, and it gets added to the file system. But when I try to edit it, I get the same error as before. Very strange. 

Any ideas?