CRM API searchRecords : Error 4500

Hi,

This is failing with error 4500

https://crm.zoho.com/crm/private/xml/Accounts/searchRecords?authtoken=someAuthToken&scope=crmapi&criteria=(Employees equals 0)

Why ?

<?xml version="1.0" encoding="UTF-8" ?>
<response uri="/crm/private/xml/Accounts/searchRecords">
  <error>
    <code>4500</code>
    <message>Problem occured while processing the request</message>
  </error>
</response>