When uninstalling Raiser's Edge on a workstation or server, you may receive the following:
Error 1500. Another installation is in progress. You must complete that installation before continuing this one.
In order to resolve this error message, allow for any other installation process to complete. This message can occur if another program is uninstalling or installing on the machine. Should the issue persist after all installations have ended, reboot the computer or server where the error is occurring and then attempt the installation again.