A. Reasons this can happen :-
1. You are running an MSDN copy of SQL Server. For SQL 7 a SELECT @@VERSION will show you using the "Developer" edition. You need to remove it and re-install a retail version. See evalupgrade.txt in the FAQ for details.
2. You are running SQL Server on NT Workstation. This has a 10 user incoming limit. You need to upgrade this to the Server version.
3. You have installed SQL on an MSDN copy of NT Server - the MSDN copy of NT Server has a 10 user limit that SQL inherits. There are tools on www.ntfaq.com and www.sysinternals.com that tell you what sort of copy of NT you have. You need to uninstall and reinstall NT. See reinstallnt.txt in the FAQ for how to make this less painful.