Search Tab shows alphabet and numbers

We have a customer with search issues. Our help is WebHelp built in RH10. Our customer runs our software (and help) on a Citrix server with IE9/Windows Server 2008 R2 Enterprise. At least one user terminal has IE8/Windows XP Professional (ver. 2002 SP 3).

When they run our help and click on the Search tab, following is displayed:

Any ideas on what's causing this?