Comment options disappear

This is getting to be a real problem. I am editing an atlas. I make numerous markups and comments. About 10 minutes into a session, my comment tool options start to disappear and black squares appear where the tool icons should be. If I keep going, soon my search term results list disappears as well, and soon thereafter all the tools are blacked out. The only way I have found to resolve it is to save, close the program, then open it up again. This takes time and causes no end of problems in re-establishing my search term results list, and finding my place in the document again.
 
If there is a permanent fix to this problem, I need it. I still have a lot of editing to do on this atlas and am only half-finished. I can't be closing down the program every ten minutes. I am using Adobe Reader X on a PC with 24G of memory.