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What's the exact day of the drop? Normally, I wouldn't really be concerned with a drop in webmaster tool impressions especially after a bump up, but since you mentioned you lost traffic on Bing, yahoo and social, it does raise some flags. IF that happened around the final 3 days of the month, then you were affected by the update I mentioned which nobody seems to be talking about.... Anyway, did you check crawl errors on GWT? Did you crawl the site separately ? Did you see any problems with the index/noindex/etc? As for injected codes, the easy way is to load pages (that you lost traffic on) in google. Check the saved cache. If you got some injected codes, they'll show up there. There's really not much we can do but assume things. I do hope you could find the reason for the problem.

Why do you want to remove the file?  Are you concerned that you may have disavowed links that you shouldn't have? When you remove the file, then as Google recrawls each of the sites that were listed in your file, they will re-avow them which means that they will once again start to give you the link equity that comes from that link.  If it's a good link then you'll regain some good link equity.  (But then this begs the question of why you would disavow it to start with.)  If it's an unnatural link then at first what will likely happen is nothing as Google will not give you any benefit for this type of link.  But, if you've got enough unnatural links then the next time that Google runs the Penguin algorithm your site will look less trustworthy when it comes to links and you could see a drop in rankings. It's complicated though.  If you are already under the effects of Penguin and you filed a disavow and then you removed your disavow then really nothing would happen. I wouldn't recommend removing your disavow file unless you feel that you have accidentally disavowed links that are good ones.  If you're not sure if you've done that then you should consider having someone review your links for you and give you an idea of which ones should be disavowed.

Hi Denverish, thanks for your reply, been months since i looked at this problem. It has returned so trying to sort it out. the redirects mentioned did not work. so any suggestions. The CMS allows for 301 redirects via a form; place old url at the top of the form and the new url at the bottom and save, But as I am trying to create a wildcard 301 redirect, i am not sure what code to place in these fields..see pic tai MgrqdVB.png

Thanks for your responses Matt and Andy, very useful information and I will go into them deeper to workout what is going on with my site.  It's interesting what Andy says about older sites getting hit the mosts as we are seeing new sites with high rankings, when in the "old days" it would take ages for these sites to rank for very competitive keywords. We have not received a Google webmaster penalty, but have been hit by one of the black and white animals. We have disavowed many links and have seen some recovery, but need to see more progress. I'll check out the links above and see if it will help in understand what to do. Thanks again, ps, if anyone has any more info, do let me know. Tai