MAPIEx: Extended MAPI Wrapper - MAPI:Failed to logon

I have an application running as a Service, written by a colleague who has now left the organisation.
 
The Service did work quite happily previously but the development project was postponed and shelved. We have recently attempted to revive the project but the Service is now failing and I cannot figure out why! Needles to say the OS and machine Environment is exactly the same as previously. Any input would be most appreciated...
 
We are attempting to construct and then send an email via Outlook (2007) utilising MAPIEX. The output log shows the following;
 
22:01:58: Setting dlog path
22:01:58: Initialising MAPI interface
22:01:58: Initialising Database interface
22:01:58: Service::Init: Succeeded
22:01:58: Starting main loop waiting for files
22:01:58: MAPI Login: Outlook
22:01:58: MAPI:Failed to logon
 
I appreciate that some of this logging is our own, but you can see the gist of the MAPIEX process.
 
We have Outlook running (as we did previously when this Service worked.)
 
I am not sure how/if we can get any further information into the Log to allow a greater vision of why the Logon has failed?
 
But, generally, does anybody have any pointers as to what/why I may be encountering this problem?
 
Thank you in advance...