I have a list of 'Brands' which is a production list. I know that 'select' function does not work with prod list members however, it should work with the list top member/ highest level . But when I am using it with the highest level i.e. 'All Categories' I am getting an error that the list member or version is not recognised in the model. Please help me understand the reason/ meaning of this particular error.
As @filip.sypniewski said it could happen if you are typing the name of your top level leading to inaccuracies. What you can do is after select statement go to the list and point it to the top level instead of writing the name of the top level.
Then my friend SELECT statement can't be used. SELECT is used when you have a dimension which is in source module but not in target module. Either you get rid of the P4 dimension in target module & use SELECT or just get rid of SELECT which will not help you the way you describe your requirement. First approach should help you where you remove the P4 as a dimension from your target module.
Error that you are receiving might be because you have the dimensions matching and you are using SELECT on matching dimensions.