To repair it, close the ILLiad client, open Add or Remove Programs from the Start menu, select the ILLiad client, choose Modify, and then Repair, then reopen the client and test the Z39.50 tab. IT staff may need to run the repair.
If the repair does not work, try uninstalling and reinstalling the correct version of the Client.
If the reinstall does not correct the issue, contact OCLC Support