trying to set DSN dynamically

I'm trying the following code, but get an HTTP 500

Here's my .asp code for the DSN:
<!-- Below file, VBFunctions.inc, will do select case for deciding on proper DSN based upon session("sessionDB") or ""-->
<!--#include file="VBFunctions.inc" -->
<%
If session("sessionDB") <> "" Then
'means user is using web app, and need to pass function, FunctDBSelect(), the session object

test = FunctDBSelect(session("sessionDB"))
varDSN = FunctionDBSelect
else
varDSN = "sns_prod"

Set MyConn=Server.CreateObject("ADODB.Connection")
MyConn.Open varDSN
'also tried MyConn.Open "varDSN", but with no luck

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Here's the function in the VBFunctions.inc file:
<%Function FunctDBSelect(useDB)
select case useDB
case "ADSFO"
FunctDBSelect = "ADSFO_prod"
case "AFSS"
FunctDBSelect = "AFSS_prod"
case "CHS"
FunctDBSelect = "CHS_prod"
case "Demo"
FunctDBSelect = "Demo_prod"
case "EP"
FunctDBSelect = "EP_prod"
case "NSS"
FunctDBSelect = "NSS_prod"
case "OE"
FunctDBSelect = "OE_prod"
case "PMP"
FunctDBSelect = "PMP_prod"
case "RN"
FunctDBSelect = "RN_prod"
case "SP"
FunctDBSelect = "SP_prod"
case "SS"
FunctDBSelect = "SS_prod"
case "WI"
FunctDBSelect = "WI_prod"
case "WSO"
FunctDBSelect = "WSO_prod"
return FunctDBSelect
end select
End Function%>

dpyers,