failed to write flash memory

I’ve got an arduino pro mini (5V) board, and when I try to upload code I get the following error:

avrdude: stk500_paged_write(): (a) protocol error, expect=0x14, resp=0x00

avrdude: failed to write flash memory, rc=-4

avrdude: stk500_disable(): protocol error, expect=0x14, resp=0xe0

This started happening after the 3rd or 4th upload, and it hasn’t worked since. I don’t recall doing anything especially stupid, but it’s not out of the question. All I had hooked up to the board initially was a serial LCD and my FTDI board.

Is my arduino faulty? I thought perhaps the bootloader was corrupt, but I don’t have an ISP to try and replace it.