FAIL001 is VCO failure. Maybe programmed for out of range freqs.
That was already answered above, but its actually VCO out of lock. In addition, the software won't allow out of range freq (last version I had) and his 15x.x range is within the allowable range of both VHF splits offered on the radio.
The antenna will have nothing to do with it and its just a conincidence. Without seeing your codeplug (and I am sure there is nothing wrong with it as long as you just changed 25k to 12.5k), I am going to say you need to bring your radio to the local shop and have it PM'd.
My guess is that it just needs a good alignment and to be sure that its running current firmware - which you may or may not be able to get as the MCS is NLS from Motorola and Motorola has had a habit lately of not providing software updates or even allow you to purchase FLASHport upgrades on NLS products (which is complete BS, but thats another thread). Some of the early firmware was buggy and did things like reboot the radio randomly, not allow it to turn on here and there etc.
Now what I forgot to ask, are you getting the Fail 001 on RX or when you PTT?