Well when I asked that they told me that there werent a limit, that it depends on the memory of your devicem but that is not true. The is not logical limit on the RMS but the device has a limitation for the midlets size, if your midlet uses a recordStore too big then you will get that exception even if the device still have some memory. For example a nokia 3120 cell phone can have a maximium size for midlet of 63 kb, my app was about 52 so I run out of space when saving many data. But on my nokia 631 and on a blackberry 7290 it worked without any problem.
Which device are you using?