The RAM memory limit will be reached if you select a catalog, or do a search that results in a large number of patterns. When the limit is reached no more patterns will be loaded and a message appears. You might try narrowing your search to return fewer results.
If you have an i400 tablet, you may run into memory issues with too many patterns of very high digitizing resolution. If you have a few thousand patterns you might have this problem. You can run the library optimizer to reduce the size of the files and clear up some space.