Exchange 5.5 and Asp VBScript error

We had to reinstall Exchange 5.5 on our BDC, after which no one could access Outlook Web Access or our download asp page. Here are the parameters:

NT 4.0 SP6a
Exchange 5.5 SP4
IIS 4.0

Whenever someone tries to access OWA or the downlaod .asp the connection times out, and sometimes they get an error that reads as follows:

Microsoft VBScript runtime error '800a000d'

Type mismatch: 'Session'

/exchange/USA/lib/session.inc, line 13

When I run MS Debugger on the server, and this error occurs, the debugger pops up and points to the following line in the Session.inc file:

iFontSize=Session("iFontSize")

In the case of OWA, we tried to comment this line out; this allowed the logon.asp page to load, but when we tried to logon it times out again on another line further down in Session.inc.

The new Session.inc is a dead ringer for the old installation Session.inc (we saved the old files in a backup), but there are other differences between the two Webdata folders. Can I take the old Webdata folder, drop it into the new installation and expect it to work? Or should I be approaching this from the angle of making changes in the Session.inc? Or is there something else I'm missing altogether?

Thanks for your help.