Question: I am currently going through a tutorial using Visual Studio 11 beta. When trying to set the max length of a field value in one of my classes:

```
[MaxLength(50)]
public string LastName { get; set; }

```

It errors out and wont let me compile because the `MaxLength()` function exists in two places:

> 
> Error 4 The type '**System.ComponentModel.DataAnnotations**.MaxLengthAttribute' exists in both 'c:\Users\me\Documents\Visual Studio 11\ContosoUniversity\packages\EntityFramework.4.1.10331.0\lib\net40\EntityFramework.dll' and 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.5\System.ComponentModel.DataAnnotations.dll'
> 
> 
> 

I have tried to remove both files but that just causes more issues because other code in my project is dependent upon them.

Is there a way I can tell it to use one or the other?

**All of these approaches don't seem to be working for me.. Refer to the comments under the answers.. Any other ideas?**

Thanks

Answer: 
In case, if you are getting the same error in latest environment (VS 2017/.NET Framework 4.6.x) and with entityframeworks like 6.1 or 6.2, here is the solution;

Downgrade your entityframework to 6.0. It'll work.
This question is now the top SO answer for this question so I figured I would answer it generally here.

The `The type 'BLAH' exists in both` error often pops up in the following occassions:

**1. DUPLICATE FILES** - (often very simple) This is notoriously the case with .dll files. In most cases of duplication, deletion of one of the duplicate files is the easiest and best solution

**2. NON-DUPLICATE FILES** - (more complicated, such as the original poster's case) you unfortunately need to edit and often recompile/find alternate versions of the files so that conflicts like this do not arise. Luckily more often than not, qualifying the attribute with the same namespace will fix conflicts like this. 

*For example if your code is conflicted on something called `MaxLength` that is mentioned in several files, then qualify it on necessary files to make it very clear which MaxLength you want to use like so: `System.ComponentModel.DataAnnotations.MaxLength`. This should help to clear things up, so nothing gets conflicted when trying to run your code*