I have read a lot of tips on this, but this is the only one that works every time. It's especially useful if you have a test environment.
When an ICA client logs onto a Windows 2000 server before it is activated, or if they do not have a Windows NT/2000 machine, they will receive a 90-day temporary license. Once this license runs out they will no longer be able to connect to the Windows 2000 server. Below is a workaround that will work for the 90 days, but then you will have to repeat these steps.
Step 1: Apply Microsoft's fix
This fix needs to be applied to the Windows 2000 server. For more information you can reference TechNet Article, Q287687 - Terminal Services Licensing Enhancements.
The next step is to remove the following registry entries on the CLIENT'S machine: HKEY_LOCAL_MACHINESOFTWAREMicrosoftMSLicensingStore.
Remove both the license000 and license001 keys. Removing these keys will force the Windows 2000 server to re-assign a license for the client's machine.
The final step is to rename the icaapi.dll located on the server under winntsystem32 to icaapi.old. Once a client logs onto the server the icaapi.dll will automatically be recreated.