Can't burn roms back to back up card? Wots wrong?

[backmeuponthis]

Some one please help!

I have got a 2nd hand bung system for the colour gameboy with a "doctor gb card 4m". When I first tried the card there were 4 working games on it. I succesfully erased the games with the bung system but now I am trying to write a single rom back to the card I keep getting a "write eeprom error". What does this mean. How can I get round this. I have tried gbxtool 1.6.
Can some one out there please advise