Tom, You might want to run CCleaner's "Cleaner" followed by "Registry" before installing the Garmin software. Back up the old registry data when it asks, no harm in that. Then install Garmin. Maybe it will resolve the issue.
Just so you know, the registry cleaner removes old registries that are no longer needed. I once had some serious system issues that went away after I ran that registry cleaning feature. Old unused obsolete registeries were in conflict with good ones. Me and all other people I know who use the registry cleaner, never created a problem from using the registry cleaner, only solving problems.
Oh, and BTW: Run each program a few times because once in a while, new things come up to clean up after others are cleaned up.
Good Luck