My understanding of
"MSP 2010 will be compatible with 12.1.1 it will not be backward compatible with earlier versions of Clarity"
is that MSP 2010 will not be backward compatible whit earlier versions of Clarity
There release notes for v12.1SP 1 say under
Clients
The following table shows supported software for client machines accessing CA Clarity PPM.
■ Microsoft Project 2007 ‐ 2010, all editions
while
Using CA Clarity PPM with Open Workbench
and Microsoft Project
v12.1.0 Service Pack 1
says
Before you Install CA Clarity PPM Microsoft Project Interface
Before you install CA Clarity PPM Microsoft Project Interface, ensure that you meet the
following criteria:
■ Microsoft Project Professional 2010 is installed with the
office-kb2075992-fullfile-x86-glb.exe patch applied:
■ Microsoft .NET Framework 4 (dotNetFx40_Full_x86_x64.exe) is installed.
■ Microsoft Visual Studio 2010 Tools for Office Runtime (vstor40_x86.exe) is installed
Though that is not quite accurate according to
Clarity 12.1 SP1 & MSP 2010 Weird Behaviors
49768546
but I would not expect any of those three installs to prevent using earlier versions of MS Project on the same workstations if you uninstalled 2010 first.
I don't think the above says anything about using different versions of MS Project on different workstations to access the one and same Clarity.
Martti K.