Hi,
While I was doin modal analysis for natural freq. check of a modal, my system was not clearing the sturm check even after increasing the cutoff freq. or even by increasing the eigen values. I searched for guidelines in a application guide and also made some changes accordingly but didnt succeeded.
Can anyone advise me on the problem.

Failing the "Sturm Sequence Check" simply means there is another natural frequency within %5 of the last frequency extracted. So if the last frequency was 100hz, there is at least one more between 100 and 105, that you may want to consider.

The only way to "consider" these potential frequencies is to increase the cut-off. However, there are some models that will never pass the "Sturm Sequence Check" (such as a cantilever). Failing the "Sturm Sequence Check" doesn't mean there is anything wrong, it just means you need to think about what is going on and consider extending the cut-off.

Maybe using "consistent mass" (as opposed to "lumped mass") might help here. That's a Control Parameter setting.