Encounter "500 Unexpected Error" when admin account access to ECP

Question

Symptom： 
In Exchange 2013, when using admin account to access ECP, you will get an error “500 Unexpected” as below. However, when using the same account to access OWA, everything is ok, and other normal accounts can access OWA also.
At the same time, if you check the event log, you will get the following error:
Current users: “yourdomain.com/User/admin”Request for URL 'https://servername.yourdomain.com:444/ecp/default.aspx(https://servername/ecp/)' failed with the following error: System.Configuration.ConfigurationErrorsException: “                                               
” (hexadecimal value 0x03)is an invalid character. Line 1, position 1 (C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\ecp\quarantine\web.config line 1) ---> System.Xml.XmlException: “                                               
” (hexadecimal value 0x03)is an invalid character. Line 1, position 1     System.Xml.XmlTextReaderImpl.Throw(String res, String[] args)     System.Xml.XmlTextReaderImpl.ParseRootLevelWhitespace()    
System.Xml.XmlTextReaderImpl.ParseDocumentContent()     System.Configuration.XmlUtil..ctor(Stream stream, String name, Boolean readToFirstElement, ConfigurationSchemaErrors schemaErrors)     System.Configuration.BaseConfigurationRecord.InitConfigFromFile()
Cause：
According to the error information, there are some invalid characters in the file (C:\Program Files\Microsoft\Exchange Server\V15\ClientAccess\ecp\quarantine\web.config ).
In Exchange Mailbox server, when we open this file with notepad, we will find that all the content are garbled. That is the cause.
Solution: 
1. Try to copy the following code to replace the contents of the file, and save it.
2. Restart mailbox server.
<?xml version="1.0"?>
<configuration>
  <location path="Quarantine.slab">
    <system.web>
      <authorization>
        <allow roles="Get-QuarantineMessage@R:Organization"/>
        <!-- Deny everyone else -->
        <deny users="*"/>
      </authorization>
    </system.web>
  </location>
  <location path="EditQuarantineAdvFilter.aspx">
    <system.web>
      <authorization>
        <allow roles="Get-QuarantineMessage@R:Organization"/>
        <!-- Deny everyone else -->
        <deny users="*"/>
      </authorization>
    </system.web>
  </location>
  <location path="QuarantineDetails.aspx">
    <system.web>
      <authorization>
        <allow roles="Get-QuarantineMessage@R:Organization"/>
        <!-- Deny everyone else -->
        <deny users="*"/>
      </authorization>
    </system.web>
  </location>
  <location path="QuarantineSDO.aspx">
    <system.web>
      <authorization>
        <allow roles="Get-QuarantineMessage@R:Organization"/>
        <!-- Deny everyone else -->
        <deny users="*"/>
      </authorization>
    </system.web>
  </location>
  <location path="ReleaseQuarantine.aspx">
    <system.web>
      <authorization>
        <allow roles="Release-QuarantineMessage@R:Organization"/>
        <!-- Deny everyone else -->
        <deny users="*"/>
      </authorization>
    </system.web>
  </location>
</configuration>
Reference: https://social.technet.microsoft.com/Forums/zh-CN/74a108a8-21f3-4f5e-8fee-94942698797a/exchange-2013ecp500?forum=exchangeserverzhchs
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Answer 1

Hi,
According to your description, I understand that open a shared mailbox and modify the setting of Outlook Voice Access by OWA, then return an error “500 unexpected error”.
If I misunderstand your concern, please do not hesitate to let me know.
Basis on my testing, run Enable-UMMailbox to enable UM feature for shared mailbox, and enable shared mailbox account in AD. Then login OWA to double check the setting of Voice mail, everything is OK.
However, I get the same error as your mentioned when login another account in OWA and open shared mailbox to modify the setting of voice mail. Also, I get same error when doing this way to access another mailbox.
I find an similar thread about your question, it may be caused by the license of shared mailbox. For your reference:
http://community.office365.com/en-us/f/148/t/160652.aspx
Best Regards,
Allen Wang