Can't insert image into PDF

I'm using Adobe Acrobat Pro on a PC. About three days ago, I started getting an error message while trying to add images. It doesn't matter what format the image is in. When I try to insert the image, I get an "unknown error" message (see attachment) and I'm told "the selected image could not be converted and placed in the document." Nothing has changed with respect to my system in the last few days. Any help would be appreciated. Thanks.