Note - This was changed in version 1.5.248 released on 8/5/2014. Graphics are converted in the background to the proper type with no software issues. You can download the latest version from here.
If you just created a new screen template and added any new images or graphics make sure they did not use interlaced or progressive compression. Booth is compatible with most graphic formats such as .JPG, .PNG, and .TIF but any of those formats with interlaced or progressive compression will cause issues in the current version of Booth. Booth is also not compatible with 16 or 24 bit files, only 8 bit. Some graphics available on the internet use these options. To test and see if this is the cause, remove any graphics you added from the screen template and then click Start Booth and see if the issue goes away. If it does then you can open the graphics in Photoshop and do a save as and un-check progressive or interlaced then add them back to the template.