When using TFS, the build server needs the key registered under the TFSSERVICE user.  To do that, use Control-Register.exe from under 
 
C:\Program Files (x86)\Keyoti Inc\RapidSpell Desktop .NET v6\.NET4_DLLs
 
This requires Keyoti.RapidSpell.NET4.dll to be in the same folder when run.  (If your application is referencing the .NET2 Keyoti DLL then run 'Control-register.exe' from the .NET2_DLLs folder instead)
 
The simplest way to do this is to install RapidSpell on the server, but it's not required, the EXE and DLL can be copied over.  Then use "Run As..." on Control-Register and choose TFSSERVICE.

When the application is compiled, the license is read from the build process account’s IsolatedStorage and the license is embedded in the EXE.  At that point, it doesn’t matter who runs the EXE or where, because the license is read from the EXE at runtime.

Information for build servers running under the system account

If you find you’re unable to use “Run As…” for the local system account then you can follow these instructions;

Download PSTools (from SysInternals, owned by Microsoft) and extract PSexec.exe to a folder on the machine.

Download from TechNet http://technet.microsoft.com/en-us/sysinternals/bb896649

Download from Keyoti http://keyoti.com/kb/attachments/pstools.zip

Open the CMD prompt using “Run as Administrator” and open the directory containing PSexec.exe

Type;

psexec -i -s cmd.exe 

(-i is for interactive, -s is to run as system)

Then launch Control-Register.exe from the new CMD window, or launch it from the Psexec command instead of CMD.

If you continue to face problems, changing the build process to run under a regular user account has been shown to help.