Romeo BLE Mini Bootloader Problem

I suddenly seem to be getting the following error whenever I try to upload using Arduino IDE 1.6.9:

avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x30
avrdude: stk500_getsync() attempt 2 of 10: not in sync: resp=0x0d
avrdude: stk500_getsync() attempt 3 of 10: not in sync: resp=0x0a
avrdude: stk500_getsync() attempt 4 of 10: not in sync: resp=0x20
avrdude: stk500_getsync() attempt 5 of 10: not in sync: resp=0x0d
avrdude: stk500_getsync() attempt 6 of 10: not in sync: resp=0x0a
avrdude: stk500_getsync() attempt 7 of 10: not in sync: resp=0x30
avrdude: stk500_getsync() attempt 8 of 10: not in sync: resp=0x0d
avrdude: stk500_getsync() attempt 9 of 10: not in sync: resp=0x0a
avrdude: stk500_getsync() attempt 10 of 10: not in sync: resp=0x20

I suspect it could be an issue with my bootloader. I can confirm that I have the latest firmware, using the correct port and board number. I have tried to upload using different computers and cables. I also used another Arduino UNO without a hitch.

I was wondering what could be causing this problem; if it is the bootloader, how would I repair it using another Arduino UNO? - it seems pretty straightforward when pairing two UNOs together, but it seems that it will be a little more tricky for a Romeo BLE Mini, since there are many pins missing.

Thanks in advance for all the help.