I need help with Workgroup on XP pro

I work in small hospital. I a workgroup set up with 3 computers in the workgroup. One of computers is running american health tech software, which we use to keep track of our residents make facesheets, file MDS for billing etc. I’m trying to get another computer in the workgroup to access the american health tech program. So I followed the instuctions that AHT gave me and it worked fine for a day. Then someone installed explorer 7 ever since then when I launch the AHT program I can only access 1 module within the program. I get this error when I try and access the other parts in the program “C:\programfiles\american healthtech\ltcnetrun\AHT.BusinessSy.dll is denied” any ideas? anybody