Javascript Timer: Span with class=datetime not found within the timer span.

after upgrading tot 7.16 i'm always getting an error:

Javascript Timer: Span with class=datetime not found within the timer span.

in the log is mentioned

theme key "JS timer" not found.

I've clear my cache a lot times, but nothing helps.
Safari does work, IE and FF not.

I didn't found any solutions that worked in the other issues.

Any suggestions?

thx