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pls check out the values you pass to the segment registers. May be you miss to put some value onto the stack or to return some value? May be you have some junk in a field?
The gdt limit is calculated like this:
(Nr of Descriptors * -1.
If you have 8 descriptors in your gdt, you'll have a limit of 8*8 (=64) -1 = 63 (hex 3f).
If you want to increase the limit: add descriptors to the gdt. This is the only valid way to increase limit of gdt.
-1. 