I know crosstab queries have some special rules, like declaring variables. It's been awhile since I've worked with them and I can't recall how to deal with this particular problem.
I am using this crosstab as a rowsource for my report. The column heading field, SampleID, can fluxuate between 2 and 8 columns of data, so my report has 8 columns to receive it. This only works if the query generates all 8 column. Anything less will generate a Microsoft Access database engine error. I seem to recall there is a way to tell the query to generate extra predefined columns as needed, but I can't remember how.
Does this ring a bell? I hope so.