Can only upload one sketch

I have a board with an ATmega328P connected to an FT232HQ.

I use an Arduino Uno for Arduino as ISP to program the boot loader into the target board.

I tel the IDE that I have an "Arduino Nano" with ATmega328, connect to the target board and select the new port.

I can upload a sketch just fine and it runs fine but if I try to upload again it fails with:

avrdude: stk500_recv(): programmer is not responding
avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00

But if I re-download the boot loader it will again let me download a sketch once...

Anyone have any ideas?

I typically burn the bootloader before each upload.