It sounds like you encountered an assembly binding issue in IIS, and updating the web.config file resolved it. This is a common scenario when the application relies on specific versions of assemblies that differ between your development and production environments.

The dependentAssembly elements you added specify the assembly identities and the binding redirects, which instruct the .NET runtime to use the specified versions of the assemblies when the application requests them. Here’s a quick breakdown of what each part does:

assemblyIdentity: Identifies the assembly by name, public key token, and culture. bindingRedirect: Redirects requests for older versions of an assembly to a newer version, ensuring that the application uses the correct assembly version. It's a good practice to regularly compare your development and production configurations to avoid such issues. If you're working in a team or deploying frequently, consider implementing automated checks or using a deployment strategy that includes syncing configurations.

If you need any further assistance or have more questions about IIS or web.config, feel free to ask!