Access a SQL app in a server from a computer in the same network

I have an SQL app installed in my server, I access it from other computers in the network by mapping the drive, copying a file to the local computer and running locally the app. It works in all computers except one a new computer. I get this error:
file access error
file (dboomssys) could not be opened.
erron SOL Server does not exist or access denied.
ConnectionOpen (ConnectO). (08001).