Cannot Embed Interop Types from Assembly
<p>I know that similar questions have been asked on here before, but I'm not sure they actually solve my problem, unless I'm misunderstanding them.</p>

<p>I've been working on an application this morning and not had any issues building or rebuilding the solution, but after going for my lunch and then coming back (I left the program open), I suddenly am unable to build it, since it is returning 3 errors, the likes of which I've not come across before.</p>

<p>Error 1:</p>

<blockquote>
  <p>Cannot embed interop types from assembly 'office' because it is missing either the 'ImportedFromTypeLib' attribute or the 'PrimaryInteropAssembly' attribute.</p>
</blockquote>

<p>Error 2:</p>

<blockquote>
  <p>Cannot embed interop types from assembly 'office' because it is missing the 'Guid' attribute</p>
</blockquote>

<p>Error 3:</p>

<blockquote>
  <p>Unable to load referenced library 'C:\WINDOWS\assembly\GAC_MSIL\Office\15.0.0.0__71e9bce111e9429c\Office.dll': The system cannot find the file specified.  C:\WINDOWS\assembly\GAC_MSIL\Office\15.0.0.0__71e9bce111e9429c\Office.dll   </p>
</blockquote>

<p>What is causing these errors to suddenly arise?</p>

<p>After checking in Project Properties > Reference > Add > COM, I can see that Office 15.0 Object Library is referenced. So what do I do? It just seems weird that they came about whilst the application was open?</p>