title: Scopus500Error: Error calling Solr Search Service
body: <p>when I used pybliometrics to get the co_authors, sometimes I get this error, but sometimes not
  I want to know why and how to solve it.</p>
  <p>Traceback (most recent call last):</p>
  <pre><code>File &quot;G:\dissertationdatabase\iteration3\iteration3.py&quot;, line 16, in &lt;module&gt;
      coauthors = pd.DataFrame(au.get_coauthors())
  
    File &quot;C:\ProgramData\Miniconda3\lib\site-packages\pybliometrics\scopus\author_retrieval.py&quot;, line 289, in get_coauthors
      res = get_content(url, api=&quot;AuthorSearch&quot;)
  
    File &quot;C:\ProgramData\Miniconda3\lib\site-packages\pybliometrics\scopus\utils\get_content.py&quot;, line 97, in get_content
      raise errors[resp.status_code](reason)
  
  Scopus500Error: Error calling Solr Search Service
  </code></pre>