Sharepoint Unable to display web part error on web parts with conditional formatting.

Hi everybody,

I have a Sharepoint Server 2010 enviroment, that was working fine. However, since last week, some webparts encounter the following error:

"Unable to display this Web Part. To troubleshoot the problem, open this Web page in a Microsoft SharePoint Foundation-compatible HTML editor such as Microsoft SharePoint Designer. If the problem persists, contact your Web server administrator."

These webparts contain list views edited in Sharepoint Designer 2010 to color code some information like task status, due date, etc.

So far i couldn't find a way to fix this and i'm asking for your help.

Thanks,

Alex