Visual Studios 2015 Error When Deploying and on Se

Question

I am experiencing a very strange error at the moment. The main issue I am having is running a .rdl (VS 2015) from a reporting server. I get the following error when trying to run the report:

An error has occurred during report processing. (rsProcessingAborted) Query execution failed for dataset 'DataSet1'. (rsErrorExecutingCommand) For more information about this error navigate to the report server on the local server machine, or enable remote errors

Here is where things get weird:

Only sometimes when I run this report, I get the following error in VS 2015, but it never happens on the first run:

[rsCollationDetectionFailed] The data extension used for the data source ‘Data_Source_1’ failed to detect the default collation properties for the connection. Details: System.InvalidCastException: Specified cast is not valid. at Microsoft.ReportingServices.DataExtensions.SqlGetCollationProperties.GetCollationProperties(IDbCommand command, CultureInfo& culture, Boolean& caseSensitive, Boolean& accentSensitive, Boolean& kanatypeSensitive, Boolean& widthSensitive) at Microsoft.ReportingServices.DataExtensions.SqlConnectionWrapperBase.GetCollationProperties(String& cultureName, Boolean& caseSensitive, Boolean& accentSensitive, Boolean& kanatypeSensitive, Boolean& widthSensitive) at Microsoft.ReportingServices.OnDemandProcessing.RuntimeDataSource.MergeAutoCollationSettings(IDbConnection connection)

Again, this warning does not occur during the first run, it only occurs sometimes on every run after the first run (restarting VS 2015 allows me to run it again the first time without the warning).

I have other reports in the same folder on the reporting server using the same data source. I am not sure if the warning is connected to the reporting server error, as I still get the result set in VS with the error. SQL query runs fine IN SSMS 2014.

Any suggestions? This is driving me crazy...