Yes it was allowed but now it's not but it seems to be a general ban and not just specifically to stop access to the CX lounge. CX can just stop you entering anyway but as I said surely it's best to stop people from even getting to the CX lounge door/
It would be silly to stop someone going through if they said they wanted to use the CX lounge but would allow it if you said you i wanted to go to the AMEX lounge.