lost access to network files

I've been using windows 7 for a few weeks and have been able to share files with the other computers on the network. This morning I tried to move a file from one of my computers to my windows 7 computer and got this error.

You need permission to perform this action.
I am the only user on this computer and have administrator rights. All the computers have the same user name and password. Disabling user control access did not help. I was able to go on the other computer and move the file I wanted to this computer. What happened.

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