Problem uploading file

[Camilla]

I'm new to CMSimple, and had to replace a pdf-file today.
It should be fairly simple, but I keep getting a warning: Could not save file ....

Currently we have 918,4 KB data, and the file is only 60 KB, so that shouldn't be the problem.
I've tried at work with no luck using IE 7.0, and 9.0, and now at home, again with no luck, using FF 3.0.5.

The person who previously worked on the site left before Christmas leaving only the most token information.

Where do I start my search to find out why the file cannot be saved?
I've deleted the file that was to be replaced without problems.

[harteg]

Check that the download folder is writable (chmod 777)