Failure to download software updates and IP blacklisting

SOme setting on my computer is stopping me from downloading iPhone software and Office for Mac software updates (network time-out and 9006 errors). My IP address is also repeatedly being blacklisted at my web based ISP (they say because of my file sharing settings!). I am at a complete loss! I do not run any anti-virus or malware program. Is it my firewal setting? I have also tried to turn off Airport and effect downloads via ethernet cable directly to my router. Any assistance would be greatly appreciated. My firewall log (see extract below) is full of stuff - mentions Dropbox data and nmbd data amongst other things - is this perhaps the problem? HELP!!!!

Apr 3 14:15:35: --- last message repeated 1 time ---

Apr 3 14:15:35 IDs-iMac Firewall[53]: Deny nmbd data in from 192.168.0.6:137 uid = 0 proto=17

Apr 3 14:15:53 IDs-iMac Firewall[53]: Deny Dropbox data in from 192.168.0.6:17500 uid = 0 proto=17

Apr 3 14:16:23: --- last message repeated 1 time ---

Apr 3 14:16:23 IDs-iMac Firewall[53]: Deny Dropbox data in from 192.168.0.6:17500 uid = 0 proto=17