Since these modules do NOT share any common files it's unlikely that having both installed would cause any issues you are having with either one..
You reported this exact same error in the Super Orders thread, and I wanted to post this here as well.. Unfortunately just as I posted in my reply to you in the Super Orders support thread, the likely root cause of this error is because of another modification you have made in your store (inadvertently or intentionally).
It's POSSIBLE that this is related to your WordPress Integration issues. (the "
headers already sent by" is a common WordPress error. This is particularly true if you are using the WOZ module which makes changes which could cause this error -- in which case you should try to track down the cause by posting your questions inthe WOZ support thread) Since I cannot see your store files I cannot say for sure what is cause of the errors you are getting..
I can say this for sure, it's likely that the error you are reporting "
headers already sent by" is caused by something UNRELATED to PDF Order Center or Super Orders. These modules are not the cause of the issue, rather both of these modules are ILLUMINATING an issue whose source is elsewhere in your store.
Do a search in the forum for "
headers already sent by" and you'll see this.
I did a Bing search and you can check out some of the threads on this error. Perhaps one of them contains the key to the source of the issue:
http://www.bing.com/search?q=PHP+War...form=QBRE&qb=2
Within the research results I found this post which includes some information and links from DrByte:
http://www.zen-cart.com/forum/showthread.php?p=622932