Slowing down Zdoom startup...

http://img139.imagevenue.com/img.php?image=590064875_zdoom_122_152lo.jpg

When Zdoom starts up, it sometimes shows you certain errors that the wad has - but they go so fast that you can't really see what they are without having to constantly press print screen and hope for the best.

Is there a way to make these messages appear slower?

After the game has started, open the console and scroll back up (if you need to). The messages will be there.

If you want to save the messages in a more permanent way, start the same with a log file and all console output will get saved to a text file. An example command line for doing this would be:

zdoom -file mywad.wad +logfile mylog.txt

That will save a file called mylog.txt in the same directory as zdoom.
(note it uses a + instead of a - in front of it)

Create, in the ZDoom directory, a file named autoexec.cfg and in it put this text line:

logfile log.txt

From now on, a log will be saved all the times.