linear buckling analysis

[FB83]

Hello,
I am new to Ansys, I'm studying an iron structure of two floors.to make the model I have used the BEAM44.the structure is pendular.I apply a distributed loads on the Beam and, after static analysis, used this strings to do a buckling analysis.
/SOLU
ANTYPE,BUCKLE
BUCOPT,LANB,1
MXPAND,1
OUTPR,NSOL,ALL
outres,all
SAVE
SOLVE
FINISH
but this not converge.
so I changed the BUCOPT option so :
/SOLU
ANTYPE,BUCKLE
BUCOPT,LANB,4,100
MXPAND,1
OUTPR,NSOL,ALL
outres,all
SAVE
SOLVE
FINISH
in this way I've just obtain 2load factor in the range of4.
I made this change because I'm working with the same model in sap2000 and the first load factor in sap2000 is 4,37.

Would appreciate any help anyone can offer.

Thanks,

FB83