I am getting the following message after installing Vray for Unreal into v 2021.1 as indicated in the instructions, and when directly installed from the Chaos download.
After enabling the Plugins this error message appears when loading the project, and I am unable to access the project unless I delete the Vray Plugin folder from the install directory.
I think that you need to install vray firstly on normal unreal 25 editor in the following folder [installation path]\Engine\Plugins\Marketplace
as mentioned in the aximmetry documentation
https://aximmetry.com/wiki/index.php?title=How_to_Install_Third-Party_Code_Plugins_From_the_Unreal_Engine_Marketplace
then you need to open unreal for aximmetry and then click on aximmetry -> install plugin from toolbar.