Error Messages: "ArcEngine needs to be upgraded" or "The install has detected an existing ArcEngine installation"

Problem/Symptom:
Trying to install Oasis Montaj or Target v7.0, and I get error messages saying that the current version of ArcEngine is 9.1, and this needs to be upgraded. The installation of Geosoft then quits, and I cannot proceed from here (and thus cannot install Geosoft).

Or, I am unable to install Oasis Montaj or Target v7.0 since the install has detected an existing ArcEngine. How do I proceed?

Environment:
This resolution applies to users that are upgrading to Oasis Montaj/Target v7.0, with an existing version of ArcGIS 9.0, or 9.1 on their computer.

Resolution:
Either upgrade the current version of ArcGIS to 9.2, or uninstall ArcGIS all together, and let the ArcEngine 9.2 install from the Geosoft CD.
If you do not wish to (or cannot) upgrade or uninstall your current version of ArcGIS, please roll back to Oasis Montaj/Target v6.4.2 (Target for ArcGIS v2.2.2).

Root Cause:
Oasis Montaj and Target v7.0 are only compatible with ArcGIS 9.2. Older versions of ArcGIS will be unable to run, since the dynamic library links (dlls) are not recognised. When you install the new version of Geosoft, ArcEngine 9.2 is a required component. Therefore you will need to upgrade ArcGIS to v9.2, or uninstall it all together (for the time being), allowing ArcEngine 9.2 to be installed. You may then be able to reinstall your version of ArcGIS.

Geosoft is currently working on a resolution to allow users the use of ArcGIS 9.0 or 9.1.