Failed to enumerate changes in the filtered articles.Then try syncing from the command line using replmerg. Not only does it, strangely, have a higher chance of working correctly, but it also shows you valuable information that can be used for debugging. To use replmerg, right click on the publication and go to Agent Properties. Then click the Steps tab and there should be a job called "Run agent.". Select that step and click Edit. There should be a long line of text in the command box. Highlight it all and copy it (ctrl+a, ctrl+c), then open a command prompt (windows key+r, cmd) and issue this command:
cd \Program Files\Microsoft SQL Server\80\COMNow type: replmerg and then right click on the command prompt to paste. If you can't paste, go to the command prompt properties (alt+space, p) and make sure Quick Edit is checked (q) then apply and try again.