Google Webmaster report shows I have Duplicated Title Tags and Crawl Errors. Using 3rd party SEF component, I removed the duplications and 301-redirected the URLs. A week later, the duplications were reduced, but the number of crawl errors remained. Can someone explain why ?

No!

Because we have no idea what those "crawl errors" might be.

Please post the pages with their errors and we can help

Originally Posted by pxzosap

Google Webmaster report shows I have Duplicated Title Tags and Crawl Errors. Using 3rd party SEF component, I removed the duplications and 301-redirected the URLs. A week later, the duplications were reduced, but the number of crawl errors remained. Can someone explain why ?

It sometimes takes several weeks, even a month for things to "roll off" the crawl error pages (as well as other pages in WMT). The pages in WMT are NOT updated real-time. They are updated at random intervals, some more or less frequently than others. Just ignore them for now. They will eventually disappear.