llvm dev - May 2010 - [LLVMdev] Error while running my pass with opt

Hi,

When I try to run my pass with opt , I get the following error :

opt: 
/home/ambika/llvm_3/llvm-2.6/include/llvm/PassAnalysisSupport.h:203: 
AnalysisType& llvm::Pass::getAnalysisID(const llvm::PassInfo*) const 
[with AnalysisType = llvm::DominatorTree]: Assertion `ResultPass && 
"getAnalysis*() called on an analysis that was not "
"'required' by
pass!"' failed.


Can anybody tell as to why this error comes?

regards,
Ambika