I. General questions
1. Are you using the correct voltage
for each game?
2. Did you test if both cartridges are working when used with a real N64/GB?
3. Are the contacts clean?
4. Which kind of Retrode (1 / 2) and which firmware version are you using?II. About the N64 game
If it wasn't the voltage: Maybe the test cartridge's flash chips require unusual bus timings. AFAIK, the first four bytes stored in an N64 game cartridge indicate how fast it can be accessed.
The Retrode's size detection may fail if those four bytes have an unusual value. And since the Retrode is using fixed timings, it is possible that these are too fast for the flash. Though the Retrode tends to be slow compared to the typical timings used in N64 games.
You probably tried the following settings:
1. the first four bytes (as viewed in a hex editor, for example) from the ROM file and
2. the exact file name obtained with these settings.III. About the GB game
We are talking about a classic GB (or maybe GB Color) game, not GBA, right?
How do you know that the size of 32 kiB (like Tetris) is correct?
Please open the ROM file in a hex editor and post the bytes from offset 140 to 14F hex (320 to 335 decimal).