At what rate has the traffic diminished?
Generally, changing the URL structure of a site and 301ing old to new will result in some traffic loss initially, which should return over a number of weeks to near normal again (there is a PR loss when following a redirects, so rankings probably won't be 100% what they were).
A very simple example, I recently changed a site from WWW to non-WWW. Result was about a 40% drop in traffic after a few days, with a 10% increase week on week after that for perhaps 4-5 weeks. The site stablised around 95% normal traffic at the end.
That's the trend you should be seeing if the issue is relating to your redirects. If the pattern is different, then the problem most likely is with something else.
Could be anything really. I just had a quick look at the site you mentioned above and the couple of things that stood out were;
1) Server was down - a few connection attempts just now and pages didn't load.
2) Use of misspellings in optimisation.
Potentially those could send out negative signals to Google. However, I'd say Google is smart enough to ignore the occaisional server outage, so unless that's a consistent problem, I don't think it would affect your rankings. The misspellings may be a minor sign of optimisation and could be associated with spam sites that list variations of keywords. However, for an old site like yours, it's also likely that the age / authority outweighs this potential issue.
On further inspection, it looks like your CMS is duplicating some content. I won't post the full URLs as mods will likely snip all references, but;
1) Is product URL - /product_###.html
2) Is index.php page - /index.php?_a=viewProd&productId=###&review=write
3) Is variation on product URL - /product_###.html?review=read
So, I'd hazard a guess that a combination of the structure changes and multiple URLs for same content is confusing Google. The dillution effect would mean that an individual page may not rank as well. And if Google is slowly discovering the new URLs, then the impact might be a gradual decline in traffic.
The URL parameters feature in Google Webmaster Tools can help here (you can use to get Google to ignore URL variation number 3).
Solving the remainder of the issues depends on what the actual problem is. Which of the two remaining URLs is the "proper" version? The index.php or the folder structure version? Either 301 old to new, or use rel=canonical to resolve it.
Hope this helps!