well, the error message sounds clear to me: there's a (temporary) dns problem on your side..
can you resolve apt.sw.be from your SME?
dig apt.sw.be
you should get something like:
[root@srvsrv ~]# dig apt.sw.be
; <<>> DiG 9.2.4 <<>> apt.sw.be
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18481
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;apt.sw.be. IN A
;; ANSWER SECTION:
apt.sw.be. 60 IN CNAME dag.freshrpms.net.
dag.freshrpms.net. 157 IN CNAME dag.ie.freshrpms.net.
dag.ie.freshrpms.net. 157 IN CNAME ie.freshrpms.net.
ie.freshrpms.net. 157 IN A 193.1.193.67
;; Query time: 104 msec
;; SERVER: 10.0.0.12#53(10.0.0.12)
;; WHEN: Thu Jan 13 15:20:44 2011
;; MSG SIZE rcvd: 109