The issue is actually Internet Explorer, not Outlook.

I've found that this condition only happens in Outlook when opening HTML
formatted emails. I've never had it happen with plain text nor rich text
emails.
Oddly, even with HTML emails, I can forward or reply and pint that
in-process forward/reply window without issue.
The "error: 54" concurrently happens in IE8 when trying to print a
fully-loaded webpage (ex. google.com).

Chances are that you upgraded to IE8 (Internet Explorer 8) and did not go
through the initial configuration process when launching IE8 for the first
time.
Launch IE8, go through the initial config, restart IE8 and Outlook and see
if you message goes away.

If the "error: 54" remains:
1. If you want, I'd first suggest you Reboot the system (yes, I know a
reboot alone will not fix this)
2. Login as ADMINISTRATOR. Note: even if your PC user is in the PC's group
of administrators, it wasn't enough for me to do the following as that PC
user.
3. When in as ADMINISTRATOR, start IE8.
3a. IF you have previously congifured IE8 under the administrator ID, then
reset its settings with: TOOLS > INTERNET OPTIONS > [tab ADVANCED] [RESTORE
ADVANCED SETTINGS] ..and.. [ [RESET]>[RESET] (wait while it does its
work)[CLOSE] >[OK] ] ..and.. [APPLY] ..then.. [OK] then close and restart
IE8.
3b. Answer all the IE8 initial configuration settings again.
4. Logoff and logon as the user again.
5. When in as the user, launch IE8. I've consistantly had to do the
configuration of IE8 all over again for the user, even though I did it before
logging in as administrator. So, answer the IE8 initial config screens again.
6. Launch Outlook. All works fine for me from then on (as does printing
from web pages like google.com)
7. Done.