in QlikView, the Cache gets stuck sometimes and you get really strange, stubborn errors that appear even though you have already taken steps against them. In that case, you might have to restart to clear the memory.
from my experience, as datanibbler pointed out, is usual once this error shows up to keep showing out on and on. If that's the case, the only solution I've found out to avoid it is to restart the program.
Perhaps you may try to avoid this type of error by modifying the objects in order a small amount of rows is showed (in any object showing a large amount of rows, listboxes included) or, if the problem affects only in the development environment and not in the production one, by limiting the amount of data loaded.