I suppose you are using non-permanent watermark.
in some versions there is a typo:
check around line 138:
Content visible to verified customers only.
I dont know why some versions have the red bracket missing.
make sure the red bracket is there.
(not in red, just a bracket)
PS: To test if it has to do with this problem, turn the watermark off (remove the filename in ACP) - then it should work also.