Application RunAs issue after upgrading from TestComplete 12 to 14

Hi,

I recently upgraded from TestComplete 12 to 14 and I've encountered an issue when using the RunAs method when trying to run an application under a different user account - "Unable to run [application] under [account name] account"

I've checked the TC 14 exe to ensure it is run as administrator (which it is). I've also reverted back to TC 12 on the backed up copy of the project and it worked without error, so the project is unique to TC 14

Does anyone have an idea what may have changed in TC 14 that could cause this to no longer work?

Thanks

Adam