Some quattro pro "access Denied"

[blockie]

Some of my quattro pro x5 file return a "Access Denied" error when I try to open them. This has recently occurred. Any ideas?

 

[blockie]

Additional info.
These particular files are one that I access only now and then. Last time that I accessed any of them is at least a month ago, so don't know what caused or how this anomaly occurred. When I first try to open one of these files I get info that tells me it is read only or open by someone else. Neither is the case. I click OK and then get the "Access Denied" message. I have admin privileges and still can't open it. However if I switch user to the built in admin I can open it.