Drosophila FM6 balancer problem

[Miss Hong Saw Tin Amy]

I have isolated a gene,skl, on the X chromosome. The females are 
homozygous lethal and the males are hemizygous lethal. They are balanced 
with FM6. In the fly stock there is no skl males. 
The females are skl/FM6.
The mutation was generated by a P-element excision. The original fly line 
is an enhancer trap line which is viable.

The problem:
I crossed the skl/FM6 females with some C.S. flies and to my horror I got 
some surviving skl males. I have also crossed skn/FM6 females to Elp/CyO 
and TM3/TM6 and in all these crosses skl males were present in the 
progeny. It seemed like skl males are only lethal when it is over the Y 
chromosome of FM6.  In skl/FM7C-blue, there is no skl males I have no 
explanation and am totally lost. If anyone has any encounters  or any 
suggestions as to what should be the next best action to take please 
write to me. I thank you  and would appreciate any ideas.

Amy Hong
mcbhst at leonis.nus.sg