Summary:

Using Outlook Plugin Lite which shows error: The CRM Server has returned an invalid response. Try again. If the problem persists, please contact your system administrator.

Work around / Resolution:

1. Log onto CRM directly checking the url to check the protocol of the url for https or http
2. Check the registry setting value for lite Outlook plugin which is located HKEY_CURRENT_USER\Software\ACCPAC\CRM\OutlookPlugin the OutlookPort is set to to a value other than 80 for HTTP and 443 for HTTPS.
3. Update the OutlookPort value to 80 for HTTP and 443 for HTTPS.
4. Close and re-open Microsoft Outlook.