unless there is a different way to cast the path, you need to use a simpler path.

You said it is in "ProgramFiles", but this folder generally has a space "Program Files" which for some reason, SQL Server has issue with locating Linked Server files.

Try a simple root folder like "C:\Acc_Link" and see if it does not connect better for you.

I still have issues with passworded Access dbs, but if I remove the password, a simple path lets me connect okay.