Invalid files appear in shared folder after copying on host machine

I shared a folder between my Win7 host machine and virtual Ubuntu, and am trying to build a small project in the virtual machine. When it complains that its missing some files, I copy those files over from another folder on the host machine. However, those files appear as invalid files in the virtual box - if I try to ls, it outputs something like this:

ls: cannot access types.h: No such file or directory
...
-????????? ? ?    ?          ?              ? types.h

However, if I copy other files, they appear normally. It appears that g++ trying to access the file before it is created messes something up and I can no longer copy that file without restarting the virtual machine, which gets pretty time consuming if I have to do that for every file. Is there any way to force refresh on a shared folder?

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