Cannot perform '=' operation on System.String and System.Int32.

I dont understand where this error is coming from, and why!   basically I have a filtering by a certain piece of information in the database, below once I call the merge I get this error.
It only happens when im process a large amount of files in the database, but if I process to files in the database via data , and want to do a filter once it get to the merge it blows up,
I dont understand why

Cannot perform '=' operation on System.String and System.Int32.


         private void SetFilter()
        {
            Generic_DatatableBindingSource.Filter = TestOnly ? "IsTest = True" : "";
            if (tpmsn.Length > 0)
            {
                AddFilter("TestPositionMSN = " + tpmsn);
            }
            if (uutmsn.Length > 0)
            {
                AddFilter("UutMSN = " + uutmsn);
            }
        }

        private void AddFilter(string Filter)
        {
            if (Generic_DatatableBindingSource.Filter.Length == 0)
            {
                Generic_DatatableBindingSource.Filter = Filter;
            }
            else
            {
                Generic_DatatableBindingSource.Filter += " And " + Filter;
            }
        } // AddFilter(
      

       this.genericDataSet.Generic_Datatable.Merge(databaseDataSet.Test_Datatable);    it fails on this specific line