Theme Upload error

I get this error when trying to install a new theme using wp-admin/:
“The uploaded file could not be moved to . . .”

I’ve read several posts to this and consistently found these two suggestions:
1- set the themes folder’s chmod permissions to 777
a-I tried this aftyer an hour or so I start getting the same error, evn though chmod has been changed.
b- this creates a security hole (doesn’t it?) so I set the chmod back to 755.
2- Turn off the monthly uploads folder thingee..
a- wasn’t on, doesn’t really apply to themese anyway, does it?

I’m just using FTP to upload the themes gor now. But this is buggng me a bt.

Any answers out there?

Oh, the blog in question is Red Tide Florida/ if that matters…