Error on Saving with Xserve in Photoshop

Hi,
I am having error “Error – ‘Photoshop could not save “file” because write access was not granted’.” with my Mac OS. The error incurs while working with Xserve in Adobe Photoshop.
We have just been upgraded to CS5 and it usually happens with PSD and PSB files. I can click on the “Save As” but it will delete the file.
And sometimes it appears to have a name with AFP.
It is very frustrating.
How I can be able to fix it?
