oh yeah !!
Actually IIF will not work with VBScript. so alternatives are ... in your access database set default value of date to null and if the text box is blank dont set date in your update query OR use IF inplace of IIF

if trim(txtdate)="" then
dtsql=""
else
dtsql=",date=#" & lbldate & "#"
end if
sql="update tablename set field1=" & fieldval & dtsql & ",field2=" etc..