I'm not very much in Regex and hope to get some help from you guys:
I've got a String like this:
string match = Regex.Match(str, @"p.msochpdefault(.+);}", RegexOptions.Singleline).Groups.Value;
There are a some issues with your RegEx:
I would recomend you check a regex evaluator. There are many (also free ones) online. With such a tool you can try your regex and revise it if it doesn't work.