We have been using the server edition of QODBC successfully for a few years now, and are currently using version 7.00.00.204 with QuickBooks Enterprise Edition 2007, running on WIndows 2003 Server, SP1.  We have been running this configuration for about 1 1/2 years.  Occasionally QODBC has had a problem connecting to QuickBooks -- that is QBXMLRPEQODBCInteractive.exe and QBXMLRP2EQODBCInteractive.exe indicate Error when running TestDCOM.asp.  I am very familiar with all of the required steps, permission settings, etc, required to get QODBC to work in this mode, and when this problem occurs, I double check all of those things -- nothing is ever different.  The best way I can describe the current situation is that when the problem occurs, none of the things I try seem to make it work, but if I wait long enough, it will eventually start working again, "by itself" -- its pretty weird.  When this first started happening, it was quick and simple -- I would make everyone get out of QuickBooks, perhaps reboot the server, and everything would be okay.  Eventually, it seemed to take a number of hours before it would start working again.  Now, it's to the point where it takes a few days before it starts working again.  There isn't anything I can determine that's causing it, and nothing I do seems to make a difference -- but if I wait long enough, it will start working again.  Yes, the server is under more load as time passes, and the QuickBooks file is getting bigger (about 400MB), but there is still plenty of memory and disk available.  I generally try to address this issue when the server is not busy at all, with no change in the results. The only discernable changes to the server itself are the application of Microsoft security patches, antivirus updates, etc.  There are no Event Log items that indicate anything out of the ordinary, etc.  I can check in the evening and it still doesn't work, but early the next morning, it's working again, with no discernable changes to the server,  for example.  Any ideas?

The application I wrote is an asp.net application.  It only does one transaction at a time, opening and closing the connection each time.  Or when you say "processes using the QODBC Server Edition", do you mean IIS in this case?  Regardless, I have tried rebooting, and it doesn't help.  In fact, it was working the last time before I rebooted, but after rebooting it would not work for a few days (and then all of a sudden, started working).   Is there anything I can look at to try to figure out what is going on, or anything else to try other than rebooting?

Yes, go the the QODBC Setup Screen and the Messages Tab, click on the Review QODBC Messages anf Review SDK Messages Logs, scroll to the bottom and look for errors in both message logs.

Are you using a STA (single-threaded-apartment) threading model in your ASP.NET application?

See: ASP.NET vs Classic ASP