Here is another error I am getting ... I usually play with the xbox controller finely but when I enable the muse I always get this .. and the moust is really delayed in responses ... is there any way to fix this?

It happens to me rarely when I alt + tab. I fix it by relaunching the game.

This is a known bug introduced by patch 1.6 (that was NOT fixed by 1.7). It's not specific to Dawnguard. Every time you alt-tab back to Skyrim, the windows mouse pointer appears alongside the in-game one. Very annoying, I might add.

Hopefully Bethesda will fix it in the upcoming patch... I can understand that the Dawnguard release has led to Beth overlooking many bugs introduced by 1.6.

but Ididnt Alt tab ....

the moust tough is still very very delayed and unresponsive , luckily I am usually using a xbox pad but , when I want to use the mouse for whatever Reason I get this annoying delayed moust cursor and the other descktop cursor slightly distant one from the other ... wich is quite annoying ...