Windows XP Professional only allows 10 simultaneous connections to shares and printer spoolers. The eleventh user gets a System error #71 message. The unused connections get freed after 30 minutes which is a bit late since often you just need a few files or to print some pages but this blocks the connection for 30 minutes.
To make things better, you can issue the command
net config server /autodisconnect:3
which sets the limit to 3 minutes. You can even set this to
0 to free a slot almost instantly.
This value can also be changed in the registry. The key is
More information can be found at KB138365.
The really evil can fly to Google Cache and get a disassembled part of the
srvsvc.dll with the needed changes to disable the limit. (Only works for XP-SP2!)
The last resort is to upgrade to Windows Server. Another thought might be to connect to the shares from a Linux box and let the clients connect to this Linux machine.