"Fatal Error" unable to load modeler DLLs is the message that I receive when I attempt to open an existing drawing. I can open the cad program and start drawing a new one, but if I try to open an existing one from either my desk top icon, or while in a new drawing that is the code that I get.Any thoughts? I was just updating these drawings yesterday with out any trouble, left work and came in this morning to this.Thank you  

Refer to this article that comes directly from AutoDesk:http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=11775759&linkID=9240617If this does not solve your problem then come back and tell us.

Thank you for the tip, but it did not seem to work. I followed the instructions as you said, but no luck.Also all of the icons have changed a bit on each of my cad files that are on my desktop. Red band on the bottom of the icon with a "A" on the top gray backround

Did you change the file association designation?  What program were you using previously?

You can also try Microsoft system restore pvoided that you have created a previous restore point.It will rescue your pc to the last known best configuration .Hope it helps.

Just to follow up, I reinstalled the software and everything seems fine. Not really sure what caused it, but glad to be back.Thank you for the help!