Moises,
Sorry that you ran into this issue.
1) How did you install MyEclipse ? Is it through Pulse/All-In-One installer/ Archived Update Site ?
2) Did you install any third party plugins which might have caused this issue?
3) I recommend a quick fix using Pulse. Here are the steps :
a. Open Pulse (Start > Programs > Pulse > Pulse Explorer or download from http://www.poweredbypulse.com)
b. Login to pulse
c. Select “Eclipse 3.5 – galileo” or relevant realm from top left hand corner dropdown
d. Select your MyEclipse 8.5 profile from “My Profiles”
e. Right click on the same and click on [Re-install and run]
f. This will open a wizard which will guide you through the rest of the steps.
4) Switch to a new workspace and check if the issue persists. If yes then paste the complete error logged in the .log file which is located at <workspace dir>/.metadata/.log
5) Also attach a screenshot of the Window > Preferences > MyEclipse.
Let me know how this works for you.