Date Posting Issue

I am using an SQL 2005 database with a web-based front end written by another party. I have been having issues with the date format for months and the software provider seems to be at a loss. Basically, the display of the month and day flip (mm/dd/yy becomes dd/mm/yy). The software is an accounting package and the date issue causes major tumoil (a transaction posted May 8 becomes Aug 5 and if you try to post May 13 you'll get an error - date out of range). Each time this happens, I have to go into my web-server and restart IIS and the issue resolves itself (temporarily). I have domain admin. priveleges and interestingly, if someone else goes into the webserver with local admin. priveleges and and resets IIS, the problem is not resolved. I realize that this may be an IIS issue more than a SQL issue but I've been working on the IIS angle for months without success. A reboot of the web server will often trigger this issue but it also happens frequently without a reboot. The date format preferences on both the web-server and database server (both running Windows Server 2003) are set identically so I don't think that this is causing the issue. Thanks

Sounds frontend app uses different date format than sql2k5's default format, may need change default os date format on sql server.

I checked the documentation and the vendor shows a regional setting of English(US) and mine is set to English(Canada). I've switched it and we'll see if that does the trick. Thanks for your help.