Homegroup forgets permissions

I have a HomeGroup that continues to forget its permissions settings.

Established Homegroup on Desktop. Selected My Documents in Libraries, right click and Share with Homegroup (view & edit). I then access the homegroup with my laptop and I am able to view and edit files on the Desktop.

If the laptop goes to sleep or if I reboot either system, these permissions seem to be forgotten. I can read the files but if I try to write, I get permission errors - access denied.

If I go back to the desktop and reset it, it is fine till the next time.

I've run the troubleshooter and it doesn't find anything.

Ideas?

Paul