PI SDK filtered summaries total

Hello,

I am trying to get the amount of time a digital tag had the state "ON" in the last 24 hrs using the SDK, I am trying this but its saying

"System.ArgumentException: Cannot do summary calculation on non-numeric data"

summaries = ipidata2.FilteredSummaries(SearchStart, SearchEnd, "", "('tag' =\"ON\")",ArchiveSummariesTypeConstants.asAll, PISDK.CalculationBasisConstants.cbTimeWeighted, PISDK.FilterSampleTypeConstants.fstExpRecordedValues);