Caused by: while parsing a block mapping
in 'reader', line 12, column 3:
player:
^
expected , but found BlockMappingStart
in 'reader', line 24, column 4:
SuperVIP:
^

seem to be getting this error constantly

any ideas?

We don't provide support for GroupManager. I'd recommend switching to LuckPerms (or, if you'd prefer, PermissionsEx). If you're using a maintained version of GM, contact the maintainer.

A third option is to use the new GroupManagerX plugin