Multi value parameter and report Data

I`ve  not worked much on Multivalue parameters and i noticed one thing when i hardciode the where clause Where  company=’CYX’ I get an exact match with Data from a  Cognos Version that i am migrating to SSRS…. However when I am using @company with a multivalue parameter that’s when its not matching i dont get a exact datamatch.. What do you think ??

 I ran the Code in SSMS and I get the exact match … My report parameters are @Year='2011' , @Period='1' and @company is a Multivalue parameter. I am getting the values for this para from a Dataset 2 which gives the list of companies...

Can someone direct me on how to use this functionality?

FM