When accessing a file in an existing share, the directory which contains the file is set to read-only. So when another client tries to access it for a second time, it receives: Sorry, you have no write-right in here.
So concurrent access isn´t possible at all....
I SWAT=>Status I get: . DOS_DENY READONLY.....
There's not enough information here. Please attach give detailed
information oni how to reproduce this and attach your smb.conf.