I just wanted to share with everyone else that I've been battling with my setup for 24-48 hrs.
HP Home Server with Win 7 Media Centre and HP Mediasmart TV as extender

I believe it relates to an update that HP have done. Firstly, my TV (i.e. extender) would not connect to My Movies --> error was something like "cannot connect to server" and after searching around, I fixed it by RDP onto the Home Server and gave "Everyone" Read Access under the Share->Permissions to d:\mymovies\filestorage.

Now I can't install run Collection Management on new PCs (In addition to my central Media Centre, I run Media Centre and MM3 on all of the families 4 personal computers) --> Getting the error "cannot write to file storage on this server". For this, I have to RDP again to the Home Server and (having had enough) under the "Security" tab, I gave "Users", "Windows Home Server Users" and "Windows Media Centre" Read/Write permissions. Someone more patient than me might find that giving rights to one of these groups would work.

Now I'm working fine, but want to post the second fix in case anyone else is struggling