Paginated report error due to paramter

I published a report that had custom parameters in a query recently and came across this error:

Unable to render paginated report

Data for this report could not be loaded due to an on-premises gateway error. A query in this report may be returning a field which is not supported by the on-premises gateway. Please remove any fields containing user-defined types or unsupported gateway types and try again.Additional steps are required to view this report.

Any way I can fix this or the query so that it can load the query properly? Initially, I had the parameters filter the data after it has been loaded but that doesn't really work as there's way too many data being loaded so I'll have to filter the data on the query level. This is a snippet of the query I'm using:

SELECT ... FROM Project WHERE (COUNTRY = @pCountry)