MMS decoding problem (asn1c Compiler)

Hi all,

I know this is not directly related to wireshark but I expect that most of you will be able to help me on this one. I am using asn1c Compiler to decode MMS protocol (transported over TPKT, COTP,Session, Presentation, ACSE layers). The problem that I am having is the asn1c compiler complains of unexpected tag when I decode the MMS layer packets. I suspect that this is related to context that needs to be passed from presentation layer onwards. Can someone kindly tell me what is a context (I understand that it is used for translating abstract syntax to transfer syntax i.e actual bits, I hope I am right in my understanding) , where should I look for it in an MMS trace ? And how is it transfered (between layers) and used by them ?

Any pointers for resolving this problem are much appreciated. Thanks.