Question: When running a web application project, at seemingly random times a page may fail with a CS0433 error: type exists in multiple DLL's. The DLL's are all generated DLL's residing in the "Temporary ASP.NET Files" directory.

Answer: 
This error was due to conflict between class name of web form and wsdl stub(code behind file .cs) having the same class name i.e.

ASPX page: Dashboard 
Class: partiacl class Dashboard

AppCode/APIServices.cs: public partial class Dashboard 

Error was reproducible only on publishing the website but build and debug did not inform any error.
You should define an alias for one of your references.

In your project file `.csproj` add the following item:

```
<ItemGroup>
    <Reference Include="temp1.dll">
      <Aliases>MyAssembly</Aliases>
    </Reference>
</ItemGroup>

```

After adding the above ItemGroup, `MyAssembly` will represent a root namespace that will contain all namespaces in the assembly `temp1.dll`.

Then you can have access to the type `foo`, which is located in `temp1.dll`, as follow:

```
using MyAssembly.foo;

```