Hi Hossam
This kind of thing is tricky without a URL but lets quickly examine what you have stated above:
- not hit during on the specific panda dates
- lots of duplicate page titles
- Google Webmaster Reports no major problems
The Google Webmaster Tools & SEOMoz tools do not scan your site for duplicate content problems, it would be a great addition if they could but it would require cross referencing all the pages against each other and then the rest of the internet so I imagine it would be a bit of a challenge to do so (Rand - you guys love a challenge, right? ;)). The offshoot of this is that you can ignore the SEO advice from SEOMoz and the recommendations from GWMT in relation to your problem.
You state that you have lots of duplicate URLs yet you claim this is not the problem yet I would beg to differ. If there are duplicate URLs is there other weak or duplicate content? Do you have product descriptions that are used on other sites or on multiple pages across the site? Do you have lots of content that is repeated on multiple pages across the site?
The kind of loss of traffic and ranking whilst still maintaining visibility for brand queries smacks of one of the more aggressive duplicate content filters that I have seen at least two cases of recently. These tend to kick in once the site has been crawled so do not stick to any specific date and the result is that you are buried for popular search terms but can still rank for terms with no competition and brand related queries.
Link devaluation was mentioned above but if the drop has been sudden and severe I would suspect a penalty is far more likely rather than a slow slide over x weeks, months into the doldrums.
Without a URL we can only theorise up to a point. To do some more in depth analysis and hang some meat on this theory we need to see your web address but from instinct and the information currently supplied, it sounds like you have a duplication penalty.
This could be remedied by the following measures:
- canonical urls for any internal page duplication
- remove thin or weak content pages from the site (delete or noindex)
- remove or replace any content that is not unique to your site alone (generic product descriptions etc)
- identify any other sites that have stolen your content and request that it is removed & follow that up with DMCA request for any sites that will not play ball
Generally, review the quality of your site and it's content specifically with an eye to make sure your content is unique, not repeated internally, there are not duplicate URLs and that your content has not been stolen by other sites (google sentences from your site in double quotes for a simple check, use copyscape for something more indepth).
Happy to take another look if you can supply a URL.
Regards,
Marcus

