The error message is pretty self explanitory: Dictionary needs two types. For example:
Dictionary<string, int> myDict = ...
Dictionary<string, string> myDict = ...
Dictionary<int, int> myDict = ...
If you are only writing:
Dictionary myDict = ...
Or
Dictionary<string> myDict = ...
Then it isn't going to work.
Without the code, we can't be more specific.
[edit]code block in wrong place[/edit]