Do not just write the MSR: instead RDMSR, set bit 0 = 0, then WRMSR

[xrysf03]

Note that the single WRMSR is a crude approach.
Optimally, to avoid stomping over other, reserved, flags, you should:

unsigned long data = rdmsr(0x1FC);
data &= 0xFFFFFFFE; // set bit 0 to 0, preserve the rest
wrmsr(0x1FC, data);