This is going to be a bit vague, as I'm only just diagnosing the problem, and I'm not the sys admin for the site.  So not got all the facts.  Anyhoo....

The site has been working fine for months.  Umbraco 4.7.0 on Windows Sever 2008 R2 with SQL Server Express.  Then yesterday client accidently installed a starter pack which overwrote assets on the site.  Sooo the sys admins did a restore from backup -- at the moment I don't know exacty what they did, but my assumption that as it was a VMware server they've be restored a snapshot of the entire machine.

Anyway all looked to be working   -- site restored and working OK, able to login to back end.  But today it seems that the Templates on the site aren't showing up in the backend properly.  Although the masterpages exist on the filesystem.

Looking at the call that the backend is trying to make I see the following error:

/umbraco/webservices/TreeDataService.ashx?rnd=3e8c532d36b84866b6f9e653554e6798&id=-1&treeType=templates&contextMenu=true&isDialog=false&rnd2=25.6

Access to the path 'C:\inetpub\xxxxxx\htdocs\masterpages\umbMaster.master' is denied.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.UnauthorizedAccessException: Access to the path 'C:\inetpub\xxxxxxxx\htdocs\masterpages\umbMaster.master' is denied. 
ASP.NET is not authorized to access the requested resource. Consider granting access rights to the resource to the ASP.NET request identity. ASP.NET has a base process identity (typically {MACHINE}\ASPNET on IIS 5 or Network Service on IIS 6 and IIS 7, and the configured application pool identity on IIS 7.5) that is used if the application is not impersonating. If the application is impersonating via <identity impersonate="true"/>, the identity will be the anonymous user (typically IUSR_MACHINENAME) or the authenticated request user. 
To grant ASP.NET access to a file, right-click the file in Explorer, choose "Properties" and select the Security tab. Click "Add" to add the appropriate user or group. Highlight the ASP.NET account, and check the boxes for the desired access.
Source Error: 
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Now the restore process didn't recover all the permissions but I've since granted Full Control to the Users group.  Which is what I normally set - but that doesn't seem to have made any difference.  I've bounced the App Pool to make sure that Umbraco was picking up the new perms.  Still nothing.

Any ideas of what I should look at next?