WorksheetFunction.CountA RuntimeBinderException error
New to VSTO, know Excel's model very well... I have 

    using Excel = Microsoft.Office.Interop.Excel;

at the head of my class, and the following simple call, which compiles correctly and even appears correct in intellisense

    double usedRows = (double)Excel.WorksheetFunction.CountA(oWks.Columns[1]);

but fails at runtime with this exception

> 'Microsoft.Office.Interop.Excel.WorksheetFunction' does not contain a
> definition for 'CountA'

about which I can find little further information. What am I missing?


WorksheetFunction.CountA RuntimeBinderException error
===

New to VSTO, know Excel's model very well... I have 

    using Excel = Microsoft.Office.Interop.Excel;

at the head of my class, and the following simple call, which compiles correctly and even appears correct in intellisense

    double usedRows = (double)Excel.WorksheetFunction.CountA(oWks.Columns[1]);

but fails at runtime with this exception

> 'Microsoft.Office.Interop.Excel.WorksheetFunction' does not contain a
> definition for 'CountA'

about which I can find little further information. What am I missing?

