Try the approach shown by Annalakshmi above. It may be easier to implement and it is pretty clean.
Just recognize that 'counterName' inside "lisa.counterName.reset" is the name Annalaksmi's assigned to the dataset. You will need to change that value to the name of your count dataset. Based on the code excerpt where you show the exception, you would use lisa.Counter.reset". Based on Prem's example, the value would be, lisa.Create a Numeric Counting Data Set.reset". Case sensitivity and blank space applies....
Within DevTest 9.0/9.1, I can see the findDataset static method on DataSetManager using Eclipse. It takes an instance of TestExec and a String value of the dataset. If you are using DevTest 8.x or prior, the method may or may not be there although I think the method was available as far back as 8.5 or possibly earlier. You might also expand the scope to include Test and System Properties but not sure that will help either.