This has just happened to me as well. I have two workspaces – one of which is fine, code assist works, but in another it doesn’t. Both contain a number of Java projects.
I had already increased the memory settings as proposed in the posting linked to above:
-vmargs -Xms128M -Xmx512M -XX:PermSize=64M -XX:MaxPermSize=128M
…which doesn’t appear to have made any difference. Interestingly if I select the “Show Heap Status” option from the MyEclipse menu nothing happens…
This is quite frustrating. Does anyone have any ideas?