Problem with Mercury Messenger

A user which is on Mercury Messenger can’t talk to a user on WLM 8.5 desktop,is there a solution, it says in Mercury Messenger contact is offline even in WLM (v8.5) why is this happening?
In WLM 8.5 desktop it fails to send message and in Mercury Messenger it shows message is sent but there is no message sent in WLM 8.5 after logging in and logging out in Mercury Messenger it says the user in WLM 8.5 is online but still can’t send messages in Mercury Messenger nor WLM 8.5

try asking the mercury user to sign in making sure the “thing” (i cant remember its name) to MSNP15

I did that but this time it’s not logging into his account when he set it TO MSNP15

then i don’t know why sry