barkingcat,
Can you answer few questions for me to get a feel of your current configuration and get to the root cause.
1. Can you copy and paste your installation detail? You can get it from MyEclipse > Installation Summary > Installation Detail.
2. How did you install ME? Have you used all-in-one installer/ using pulse explorer downloaded ME/ installed base eclipse 3.4.1 and added MyEclipse 7.1.1 as a plugin?
3. Do you have any 3rd party plugins added to MyEclipse? If so, can you list them here for me? You can get it from Help > Software Updates > Add/Remove Software.
This issue might be because of incomplete/corrupted JRE. Look for myeclipse.ini file under your [MyEclipse installation dir]. Open the ini file and look for -vm argument, you should be able to see configured JRE. Can you copy and paste the contents of your config file here (.ini) Can you validate that the JRE path configured is correct?
I can recommend you to download a complete 1.6JRE and edit your config file to refer to the new 1.6JRE.
Let me know how this works out.