Maybe in the 2010 version you don't have delete rights?
The permissions I had in 2009 are the same as in 2010.
I did get some information that from our provider support that it "appears to be related to SolidWorks software performance report 559060; drag and drop of file in an Enterprise PDM vault view fails from files list to folder list. The current workaround is to use "cut and paste". SolidWorks is aware of this problem and they are working to resolve this issue."
So, "cut and paste" it is I guess.