Cannot save word document in asp.net.

[fumade]

Hi Guys,
When i try to save word document in asp.net.
it throws exception as following,

Word cannot save or create this file. Make sure that the disk you want to
save the file on is not full, write-protected, or damaged.(C:\test\test.doc)

But i do have full access to "C:\test\" folder,and the test.doc is not
readonly.

Any clues?

Thanks