SSAS Tabular Model Error: Object reference not set to an instance of an object. While trying to add tables to the tabular model
<p>I'm trying to create my first SSAS Tabular model. I'm following the steps mentioned in following tutorial:</p>

<p><a href="https://msdn.microsoft.com/en-us/library/hh231690.aspx" rel="nofollow">https://msdn.microsoft.com/en-us/library/hh231690.aspx</a></p>

<p>While trying to load the tables to the model, I get the following error:</p>

<blockquote>
  <p>Blockquote</p>
</blockquote>

<p>"!! Relationship: dbo.DimCustomer[GeographyKey]->dbo.DimGeography[GeographyKey]</p>

<ul>
<li><p>Status: error</p></li>
<li><p>Reason:Object reference not set to an instance of an object.</p></li>
</ul>

<p>!! Relationship: dbo.FactInternetSales[CustomerKey]->dbo.DimCustomer[CustomerKey]</p>

<ul>
<li><p>Status: error</p></li>
<li><p>Reason:Object reference not set to an instance of an object.</p></li>
</ul>

<p>!! Relationship: dbo.FactInternetSales[OrderDateKey]->dbo.DimDate[DateKey]</p>

<ul>
<li><p>Status: error</p></li>
<li><p>Reason:Object reference not set to an instance of an object.</p></li>
</ul>

<p>!! Relationship: dbo.FactInternetSales[DueDateKey]->dbo.DimDate[DateKey]</p>

<ul>
<li><p>Status: error</p></li>
<li><p>Reason:Object reference not set to an instance of an object.</p></li>
</ul>

<p>!! Relationship: dbo.FactInternetSales[ShipDateKey]->dbo.DimDate[DateKey]</p>

<ul>
<li><p>Status: error</p></li>
<li><p>Reason:Object reference not set to an instance of an object.</p></li>
</ul>

<p>!! Relationship: dbo.FactInternetSales[ProductKey]->dbo.DimProduct[ProductKey]</p>

<ul>
<li><p>Status: error</p></li>
<li><p>Reason:Object reference not set to an instance of an object."</p></li>
</ul>

<blockquote>
  <p>Blockquote</p>
</blockquote>

<p>What shall I do to get rid of this error message?</p>

<p>I'm using SQL Server 2014 and Visual Studio 2015 (SSDT).</p>