1) is this when taking screenshots of your browser?
1a) Is your browser Firefox?
See SC Options:
Basic Capture > Capturing options
Untick 'Capture URL' =>see if that makes a difference
2) could this be to do with your anti-virus?
I believe this has been a problem with others in the past: the AV updates, and decides to give SC a hard time.
To rule this out, can you add SC to list of excluded processes in your anti-virus ?