Unable to specify field when creating list/report layout
I'm trying to create a list/report layout that will summarize data (therefore using the Report with Grouped Data option, with both subtotals and grand totals), but I can't specify fields when I get to the Specify Subtotals page in the New Layout/Report Assistant. I click on "Specify", which opens the dialogue box "Specify Field". The top box shows "Current Table ("Name of Table") in a drop-down list, which is the table I want, but all the fields listed in the box below are grayed out and I can't select any of them. Does anyone know what might be going on? I need to be able to select a field in order to create a subtotal! The same thing happens with grand total, and anywhere else in the Assistant where I try to specify a field.
Thanks in advance for any help you can give me!