Error when I try to download a torrent

[Xilizo]

Hi. I've had uTorrent at this computer for a long time with no problems, unless me not bothering to portforward my connection throught the router I download at speeds from 100-800 kb/s and I'm connected to a 8 mb/s internet connection. A few days ago I opened a few torrents for downloading and it started with speeds at 0,5 kb/s and so on.

The problem is that it downloads at this speed in like 30 seconds, then the status turns into this error: "Error: Invalid download state, try resuming". I try to resume, but the same error appears just another minute or half later.

I save my downloads at my Iomega portable 1tb drive, and I never move the files. I haven't had any problems earlier. Please try to help me, I need uTorrent