Upload problem

I have trouble uploading files. Also I’m not sure which WordPress MU version is installed on the server.

When I try to upload a pdf-file: The file is uploaded to the media library but I get this error message.
74PHP Warning: filesize() [function.filesize]: stat failed for C:\WINDOWS\Temp\php11C.tmp in C:\Inetpub\mysite\wp-admin\includes\ms.php on line 31

When I try to uplaod a flv-file (80kb in size) I get this error message and the file is not uploaded. The errorcode is in swedish and the english translatationis something like “The file doesnt comply with the security rules. Try with another”

“Filen motsvarar inte säkerhetsreglerna. Försök med en annan.
PHP Warning: filesize() [function.filesize]: stat failed for C:\WINDOWS\Temp\php11D.tmp in C:\Inetpub\mysite\wp-admin\includes\ms.php on line 31