Vista home basic shares

I have 5 pcs setup with vista home basic. I have one pc that shares it files.
When one pc opens an excel file,word or access db from the share the other
pc's can not open the same file. Usually if you open an excel file you can
open it again with r/o permissions. The other pc's can open other files no
problem.

Home basic should allow 5 concurrent connections to the same file? Or have I
missed something within the shares. Not sure I went over this many times and
cannot find the solution. Any help would be great...