A field can only contain 1 datatype, eg a number or a string - your if statement could return a string or a number hence the error.
You either need to make the "Cancelled" a number (0 for example) or the else statement a string - you can do that by enclosing it in the totext() function. eg;
if isnull({member_count_by_parent.EE_Total})
then
'Cancelled'
else
totext(DistinctCount ({S_SRV_REQ.SR_NUM}, {S_ORG_EXT_1.NAME})/{member_count_by_parent.EE_Total}*100)
Regards,
Ryan.
Edited by rkrowland - 14 Feb 2012 at 4:44am