Eclipse runs out of memory, disables semantic check, but cant be re-enabled

Happens to me several times a day for the last month. I get the message shown below. There is no shortage of physical memory, have 11GB spare.

After this message, Eclipse refuses to compile TTCN code. Even if I go to On the fly checker preferences, restore default values. Still cant compile. Open/close Eclipse, still cant compile. Remove project from Eclipse and import again, still cant compile.

The only ways I know to fix this issue to get compiling working again is to right click the project and remove, then add again the titan project nature (which loses custom project settings), or create a new Eclipse workspace, import the project.

Java memory use is at 1.2GB according to Ubuntu System Monitor which seems unusually high.

Any ideas?