Jehan,
Sorry that you are seeing this issue.
Can you please try these settings by going to Window > Preferences > MyEclipse > Servers > Integrated Sandbox > MyEclipse Tomcat 6 > JDK. In the Optional Java VM Arguments section you can try adding :
-Xmx512M
If you are still seeing issues , Can you please open <MyEclipse spring installation directory>/myeclipseforspring.ini in any text editor and change the values based on the size of your workspace.
-vmargs
-Xmx512m
-XX:MaxPermSize=384m
If you are still seeing the issue, please try increasing the MaxPermSize and check whether that is working.
Please check this link for more information :
http://www.myeclipseide.com/PNphpBB2+file-viewtopic-t-10087.html
Let us know how it works for you.