Instead of using the field, you need to reference the column and row in the cross-tab. So, it might look like this:
"mailto:"+ GridValueAt(CurrentRowIndex, <index of email addy column>, CurrentSummaryIndex) +
"?subject=" + " Question(s) Related To Report - " + ReportTitle +
"&body= Hi " + GridValueAt(CurrentRowIndex, <index of first name column>, CurrentSummaryIndex) + ",%0D%0A%0D%0A" +
"I am reviewing the captioned report and have following questions:%0D%0A%0D%0A%0D%0A "
+ "Thanks"
-Dell