ClearCase with Rational Application Developer unable to connect

I've been using RAD for a few months now, and recently the ClearCase plugin has stopped working. Upon installation everything was gravy, but then I went ahead and installed a Adobe Flex Builder plugin which seemed to break ClearCase. I get the error message:

Connect to Rational ClearCase failed. Please ensure that the proper version of clearCase is installed with the proper patches. Consult the ClearCase SCM Adapter documentation for further details. Provider name: IBM Plugin name: Rational ClearCase SCM Adapter Plugin ID: com.rational.clearcase Version: 7.6.0.v201105111445

I should add that I managed to fix this issue once before, after the Adobe Flex install. But now it has cropped up again, this time (seemingly) unprovoked. I cannot for the life of me remember what I did to fix this the first time around. There is a similar question here on stackoverflow, but the answer didn't provide me with much inspiration.