Possible install corruption. Reinstall Soulseek (after following instructions below). Then try uninstalling again it from the Add/remove applet.
"To re-install the Soulseek client, go to the Control Panel, choose Add/Remove Programs and uninstall in the normal manner. It's a good idea to check that the Soulseek installation directory (usually C:\Program Files\Soulseek) has been completely removed, before re-installing it. At this point it's also worth checking that the Soulseek registry key has also been removed. If you're unsure how to check the registry, please ASK AN EXPERT as altering the registry can cause serious problems if not done correctly." Source - click here.
If still no joy I suggest using the Soulseek forum click here to search for an answer or start a new thread.