Example error message: "Login failed for user 'domain\username'. Reason: Server is in single user mode. Only one administrator can connect at this time."

Solution to set SQL Server to Multi-User mode:
1. Launch SQL Server Configuration Manager.
2. On the left, click SQL Server Services.
3. On the right, right-click SQL Server (WASPDATA), Properties.
4. Startup Parameters tab
5. In the Existing parameters section, click the line that is just -m
6. Remove button.
7. OK.
8. Right-click SQL Server (WASPDATA), restart.

SQL Server should now be in Multi-User mode, and you should be able to log into Wasp Configuration Tool and/or SQL Server Configuration Manager.