How to Fix ''The messaging interface has returned an unknown error. If the problem persists, restart Outlook.' Error, user has outlook 2007 connected to exchange 2010 server , I tried scan pst, configuring new profile but no luck so far. Please suggest !

Make sure Outlook is patched up to date.  If it is, try reinstalling Office.

Hi,

Please try the steps mentioned below and check if it helps:

1. Open Computer > Local Disk C > Program Files > Microsoft Office > Office 12 > Outlook.exe.
2. Right click on outlook.exe and click on Properties and then click on Compatibility tab. Uncheck the box run this program in compatibility mode for under compatibility mode, click on Apply and OK.

Note: If you are using 64 bit computer then the file location of the file will be

Computer>Local Disk C>Program Files (x86) >Microsoft Office>Office 12>Outlook.exe

Similar thread:

https://social.technet.microsoft.com/Forums/en-US/aa396c9e-0ce5-4de5-99e3-4f0d771b07e0/exchange-2007-messaging-interface-has-returned-an-unknown-error

Best Regards.