Error message help

I have a report parameter called @.OffenseCode and it is just a string
and also allows null values.
For some reason, I am getting the below error message, which I don't
know how to decipher. Any ideas?
"The value expression for the query parameter '@.OffenseCode'
contains an error: [BC30456] 'OffenseCode' is not a member of
'Microsoft.ReportingServices.ReportProcessing.ReportObjectModel.Parameters'."
Thank you!!!To access a Parameter value from an expression you will need to use the
following snytax.
=Parameters!@.OffenseCode.Value
if your parameter name is @.OffenseCode it may simply be OffenseCode in
which case you would need to use
=Parameters!OffenseCode.Value
You can check by going to the Report Menu, Report Parameters, this will
list all your parameters for the report and their names