Does the use of an underscore in filenames adversely affect SEO

[FFTCOUK]

We have had a page which until recently was ranked first or second by Google UK and also worldwide for the term "Snowbee".  It is now no longer in the top 50.

I ran a page optimization report on the url and had a very good score.  The only criticism was that I had used an atypical character in the url.  The only unusual character was an underscore "_"    We use the underscore in most file names without apparent problems with search engines. In fact they are automatically created in html files by our ecommerce software, and other pages do not seem to have been so adversely affected.

Should we discontinue this practice?  It will be difficult but I'm sure we can overcome this if this is the reason why Google has marked us down.

I attach images of the SEO Report pages

8fDPi.jpg AdLIn.jpg

[FFTCOUK]

Thanks Charles.

The link was useful.

[SL_SEM]

Underscores are not good to use in URLs as search engines do not treat it as a space or delimiter. So Snow_Bee would be considered Snowbee. I believe search engines have gotten better at figuring out when a word like this should be two words, but the best practice for this is to use hyphens (e.g. Snow-Bee).

Here is a video from Matt Cutts about it:

http://www.youtube.com/watch?feature=player_embedded&v=AQcSFsQyct8

This wouldn't cause you to drop off though especially if you ranked previously. Is it just for this one term or is it for multiple terms? I would be looking at link backgrounds to be sure there weren't any spammy links getting devalued that maybe didn't get caught before, or perhaps review the content of the page to see if it might have gotten caught by the penguin anti-spamminess updates.