OK, let's go back to basics.
What version of Exchange (find this from the general tab on the props of the exchange server in System Manager)
You added the keys as shown correctly e.g. DWORD in the right place (did you create them or create the reg file?)
Are you getting any errors on Exchange during the MM that relates e.g. the 9646 error ?
Can you add the following keys:
[HKEY_CURRENT_USER\Software\SalesLogix\MailMerge]
"DebugMode"=dword:00000001
"CleanUpFiles"=dword:00000000
Then, after running a problematic merge - look in:
C:\Documents and Settings\%User%\Application Data\SalesLogix\MailMerge\Debug
Some files will be there - can you zip them up and attach.
Then, switch off the debug with:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\SalesLogix\MailMerge]
"DebugMode"=dword:00000000
"CleanUpFiles"=dword:00000001
Let's go from there !
Mike