Running Sibelius 12 in Windows 10 with Garritan Personal Orchestra 5

When loading Sibelius 'Scanning VSTs' tries to scan over 1500 .dll files then produces the following window:

Microsoft Visual C++ Runtime Library   Windows 10  Sibelius 12  GPO 5

Program: C\ProgramFiles\Avid\Sibelius\Sibelius.exe

R6034

An application has made an attempt to load the C runtime library incorrectly. 

Please contact the application's support team for more information.

Avid say they cannot assist. I can't load Sibelius at all.

Mike