NodeXL uses the Search feature built into Windows to analyze your email, and Search is apparently finding an email address that is "ldershem" instead of the full address.
If you want to track down the particular email that is causing the problem, you can ask Search to find it for you without using NodeXL. To find emails that have "ldershem" in the To: field, for example, type this into the Search box in the Windows
kind:email AND to:ldershem
If that doesn't reveal the mysterious email, try these:
kind:email AND from:ldershem
kind:email AND cc:ldershem
If those don't turn up the email either, try using the search feature built into whatever email program you are using.