It's normal you get this error message, because the given path doesn't exist for sure. It is mistaken, because the #@# variable, given at the beginning of the Icon1 variable indicates the @Resources folder. But the explicitly written path is starting from the root of the C: drive and these two things are in conflict.
So two recommendations:
Add the exact and correct path to the Icon1 variable. If you have the .ico file into the @Resources folder, begin the path with the #@# variable and add the path after it (for instance this path may by this: #@#Icons\Icons in Use\drive-slim-raid-4disks.ico).
If the above fixes the issue and you get the variable indicating the proper path, it's ok. Otherwise try moving the whole Skins folder outside of the OneDrive folder (if it indeed is in this folder - however I am not entirely sure), because over time have been reported issues when the skins are stored into an OneDrive location. Most probably the best place for skins is the default place. If you don't really know how to move the Skins folder, let me know, for detailed instructions.
Did you get the icon working with most probably the first recommendation above?
C:\Users\User\OneDrive - Company\Resources\Icons\Icons in Use\
As far as OneDrive - I have these files set to always be on the machine. I did try it on a non-OneDrive location and saw the same issue. I just really want to be able to specify my own path to the icons.
C:\Users\User\OneDrive - Company\Resources\Icons\Icons in Use\
Alright, try this: Icon1=C:\Users\User\OneDrive - Company\Resources\Icons\Icons in Use\drive-slim-raid-4disks.ico. This is the same path as the one you had before, I just removed the not-needed #@# variable. Does this work?