disconnect when access program via vpn using ppp?

hi all, need help please, i’m running vpn server in mikrotik using ppp and it worked well, user can connect and
can access the network at my place, the trouble show when 2 users access my network via my vpn and access
the accounting program(foxpro prog-with some GUI), they had experienced disconnect from the program.
What should i check about this, i’m not give limit bandwitdh to these users or is there any kind configuration i miss or wrong ?.

Need advise please, thank’s a lot