Microsoft VBScript runtime error '800a000d'

Type mismatch: 'Session(...)'

/indir/Files/3download.asp, line 10

6 if not session(""&id&"") = True then
7 rsDownload("hitdownload") = rsDownload("hitdownload") + 1
8 rsDownload.update
9 end if
10 Session("arttirdi")(""&id&"") = True

Hata nerede ?