A strange build problem

I just copied all the files in one of my websites from a network drive to another location in that same network drive.  For some reason when I try to build a page (highlight the page, right-click build page), I get a page not found error.  I know the file exists.  In fact when I double click on the error it brings me to the page in question.  If I try a Re Build all it works just fine (Although it does build faster then expected). I even tried to add a new page.  The same thing happens with the newly added page.  I don't have this problem with the original copy.
Any help would be much appreciated.
ps. I am using asp.net 2.0
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