I followed one of your recipes and posts with the lid on etc. It just tastes like a week old pile of grass to me for some reason. Maybe its just my personal taste, I've had it in the bottle since early august and its gotten a little better, but its still take a sip and dump it. I've even tried keeping a few bottles at 34 degrees for a day or two. I do like the base beer taste sans the grassyness.
I did a little poking around, not sure if this helps you at all... This is straight from the BJCP study guide for diagnosing beer problems.
Grassy
This is the flavor and aroma of freshly cut grass or green leaves. Responsible compounds include the aldehydes hexanal and heptanal, which are produced by the oxidation of alcohols in the finished beer or the deterioration of improperly stored malt or hops. Some English and American hop varieties produce grassy notes if used in large quantities, but this flavor should not be a significant part of the profile.
Acetaldehyde
This compound has the taste and aroma of fresh-cut green apples, and has also been compared to grass, green leaves and latex paint. It is normally reduced to ethanol by yeast during the secondary fermentation, but oxidation of the finished beer may reverse this process, converting ethanol to acetaldehyde. Elevated levels are generally present in green beer or if the beer is prematurely removed from the yeast. It can also be a product of bacterial spoilage by Zymomonas or Acetobacter. Background levels of acetaldehyde can be tasted in Budweiser due to the use of beechwood chips to drop the yeast before it can be reduced to ethanol.
What I find interesting is the "can also be a product of bacterial spoilage by Zymomonas or Acetobacter". I wonder if some of those may have been working on your mash and this lead to the spoiling of the finished beer?