I tried to connect my Forerunner 10 this evening after not connecting it to the PC in a week or two. Last upload was April 3. Garmin Express failed to sync, and I couldn't open the application manually.
I tried uninstalling and installing the latest build, but the installer fails after some time with a permissions error. Clicking "Try again" does not fix the problem. This procedure does not find any problems.
This is Windows 7 64-bit. I am the administrator. No third-party anti-virus software is running.
It appears that Microsoft .NET framework 4.5.2 applied a security update to itself yesterday along with about 10 or so security updates to Windows. Based on other posts with similar problems I wonder if this had something to do with it.
Edit: fixed the problem. Running the .NET repair tool did not fix it. I had to run the .NET 4.5.2 installer from Control Panel/Programs and Features and force it to repair from there. Then I was finally able to run the GE installer.