Same error here on Win XP SP3, FF 3.6.3, GnuPG v2.0.14 (MingW32), FGPG 0.7.10.
This error happens when i try read an signed message from drafts.
1 2010-04-05 18:03:40
Re: GMail message composition is broken? (19 replies, posted in Bugs & problems)
2 2009-12-04 16:25:28
Re: Gmail - Unknown error, FireGPG can't verify this email. (8 replies, posted in Bugs & problems)
it can't verify this 
And in Gmail i have this error;
checkDock/message chrome://firegpg/content/Webmails/Gmail/cgmail2.js 594 boutonboxs[j].getAttribute("class") is null
3 2009-11-28 10:13:31
Re: Gmail - Unknown error, FireGPG can't verify this email. (8 replies, posted in Bugs & problems)
I have same problem too. Text verficition works.
4 2009-11-26 10:28:39
Re: PGP Signed Message, could not be verified. (16 replies, posted in Bugs & problems)
Hi,
I have same problem too. I am using WinXP SP3 up to date(32bit), FF 3.5.5, last version gnupg for windows and last version firegpg. It doesnt verify any signed mail even mines. Here is my ff error logs;
Hata: FireGPG-debug: [misc.EnigConvertToUnicode]undefined@1143 Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED) [nsIScriptableUnicodeConverter.ConvertToUnicode]
Kaynak dosya: chrome://firegpg/content/Core/misc.js
Hat: 82
Hata: FireGPG-debug: [misc.EnigConvertToUnicode]undefined@1143 Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED) [nsIScriptableUnicodeConverter.ConvertToUnicode]
Kaynak dosya: chrome://firegpg/content/Core/misc.js
Hat: 82
.....
.....
i have 6 error like this.
And one more question; i can't "activate inline" in gmail. i tried click "active inline for this site" in gmail. but there wasnt "deactivate inline". is this normal?
Thank you
edit: i forgot to say. just inline verification doesnt work. if i use editor, everything is fine
edit 2: here is my last establishings; inline verification doenst work any site and any sign(even activeded inline sites). but if i copy a signed mail or text to editor and then if i erase seperation between lines, it works. but inlive verification doesnt work in any site and any situation without this way.