Missing Outlook ref in Access 97/2k/XP

I have written a module in an Access 97 database which has then been used in Access 2k/XP databases to allow users to initiate Outlook and merge Access fields into an email for sending out standard receipts.

The code works fine but there is one problem. Occassionally the reference to the Outlook dll is marked as missing and the code crashes due to this. I have tried placing the dll’s in a network location and referencing them there in case they were being updated by IT. This has made no difference. Can anyone help as I am now under pressure to stabilise the systems?