Check your node and package paths to see if there is a version of archilab in an added directory (ie one version of the the package from the office standard packages on the network or a shared C drive location, while your packages are loading an conflict from your local user directory).
Also be sure you have the right Archilab version for your Revit build. For Revit 2020 you want an Archi-lab build ending in 2020 per the package notes. @john_pierson has a great video highlighting this here: How to Install the Correct Version of the archi-lab Package in Dynamo for Revit - YouTube