Could be... that would explain why it works on the 3410.
The 3410 has a smaller heap than the 7210, so in case that doesn't make much sense, I'll explain. When Nokia phones load images, they get expanded from PNGs into the device's native format. For a monochrome phone (like the 3410), images expand to a pair of 1 bit per pixel bitmaps, one for the image and one for the transparency mask. On the 4096-colour phones (like the 7210), images expand to two bytes per pixel - four bits for each of red, green, blue and alpha (opacity).
In both cases, this is irrespective of the original image format. The 3410 loads all images with a transparency mask, even if the image does not contain transparent pixels. And the 7210 will load an image in 4096 colours even if it's monochrome.
(The same goes for images created with createImage(int width, int height).)
The result is that an application that will load on a mono phone may fail on a colour phone with a larger heap size, because of the increase in its memory requirement.
If you are loading large (or many) images (which would surprise me from a 27k JAR) or creating sizable in-memory image objects, then this would explain things.
If you're testing with the emulator, you can increase the heap size by adding to the command line:
where 300000 is the size in bytes of the heap you want. (It must be in bytes, and can be from 0 to 1048576.) Standard heap size is about 200k. Of course, you can't increase the heap on the real phone, but it will at least give you an opportunity to test whether memory is the problem.
7210.exe -heapsize 300000 myapp.jad