This is a tip in case you face this situation. I guess I had done it using different jar files in the past but I could be wrong.

webMethods Version: 651
OS: windows

Scenario: When I tried to uninstall one component from the whole system ( I tried to uninstall only JDBC Adpater) using the add or remove programs tool from the control panel in windows the uninstall was successfull. Then onwards every time I ran the uninstaller it failed with this

and this

Now this is the procedure you need to follow.

Change to the folder in a command window where DistMan.jar resides.

cd webMethods_Installation\install\jars

use the command

java -jar DistMan.jar -installDir full_path_to_webMethods_installation_dir

this will help you to run the uninstaller successfully.

Good Luck

Thahir