I have much the same problem with the Private Messages mod.
I'm also using Access/ODBC.
I get the message "Table already exists" at that point in the MOD setup (table FORUM_PM).
I then created the table by hand with a dummy column, created a new MOD setup to alter the table and add all the required columns rather than create the table from scratch.
The mod functions could then find the table and columns they needed., but I get a runtime error from inc_func_secure.asp which was not touched by the mod.
The relevant bit of the MOD setup for the table is
[CREATE]
PM
M_ID
M_SUBJECT#varchar (100)#NULL#
M_FROM#int#NULL#
M_TO#int#NULL#
M_SENT#varchar (50)#NULL#
M_MESSAGE#memo#NULL#
M_PMCOUNT#varchar (50)#NULL#
M_READ#int#NULL#0
M_MAIL#varchar (50)#NULL#
M_OUTBOX#smallint#NULL#1
[END]
I'm sure the first line needs a type for the first column. Since it is taken from the MEMBER_ID, it should by rights be longint.
I've tried making it a longint column, but still get the overflow error in inc_func_secure.asp when it's called in topics.asp.
Getting the table to create correctly from the MOD setup may solve the issue (but then again, it may not).
Note:
The runtime error described above turned out to be an entirely different problem. The MOD now appears to run fine.