linksys router and ftp access

im curious, im behind a lynksis router, and dsl modem.

i am able to access multiple ftps but when it comes to my friends ftp i cant access it, the thing is, other friends that arnt behinf a router or are behind a d-link router can access the ftp...

also other people that are behind a lynksis router or other types of routers besides d-link have not been able to access the fto either..

i guess my question is, is something set up wrong on the ftp server side or is something in the routers?