The most common 500 error that will be referenced is related to 0x80070021 (#2) as in the screenshot above.
Current troubleshooting will have you edit the web.config file of the new deployment on IIS and remove the following lines. Ensure to save a copy of the web.config prior to editing.
<modules runAllManagedModulesForAllRequests="false">
<remove name="WebDAVModule" />
</modules>
After the lines have been removed and the web.config saved. Recycle the App Pool and Restart the website.
If there are still issues or the error changes, attempt to revert to the previous deployment and escalate the issue to Development with screenshots and the following details:
API URL
Servername
API Version
IIS Version
.Net versions installed w/ dates
