Dev site creates session fine, production site doesn't

[YOUFAIL]

I have two sites running on the same server (IIS7 on Win2003).Site A is my production site.Site B is a development version of site A. Aside from connection strings in its web.config file, both sites are running the same code.There are some session variables created in Session_OnStart in global.asax. I've noticed over the past couple weeks, Site A's session variables aren't being properly created. (These variables are used to populate a couple of dropdownlists) This causes the drop-downs not to auto-populate or other errors depending on the page the user is trying to hit.Site B's session variables have been working correctly. When I hit Site B, the drop-downs populate as I expect.The first thing I want to try is an IIS reset to see if this corrects the problem, but I'm wondering why my sessions wouldn't be created correctly if both sites are running the same code?