Anyone else here have an issue with changing the clock from low to high?

Using slush's pool I can cruise along fine at 30,000 Mh/s but as soon as I try to change the clock speed to high and click the reset button I get all x's, ie,

ASIC_01-16: x x x x x x x x x x x x x x x x
ASIC_17-32: x x x x x x x x x x x x x x x x
ASIC_33-48: x x x x x x x x x x x x x x x x
ASIC_49-64: x x x x x x x x x x x x x x x x
ASIC_65-80: x x x x x x x x x x x x x x x x
ASIC_81-96: x x x x x x x x x x x x x x x x

M_01-16: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_17-32: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_33-48: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_49-64: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_65-80: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000
M_81-96: 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000

Jobs:0000000000 Accepted:0000000000 Rejected:0000000000 (0:0) F1 F2 F3
MHS:00000 Utility:000 Efficieny:000.00%

Works absolutely fine until I try to overclock it, it showed this a few times but usually just fails with all x's now:

ASIC_01-16: O O O O O O O O O O O O O O O O
ASIC_17-32: O O O O O O O O O O O O O O O O
ASIC_33-48: O O O O O O O O O O O O O O O O
ASIC_49-64: O O O O O O O O O O O O O O O O
ASIC_65-80: O O O O O O O O O O O O O O O O
ASIC_81-96: O O O O O O O O x  x  x x x  x  x  x

I've been hesitant to open it up as I can't see why just overclocking it would be a hardware issue, and I might be selling it, should I ?