I keep receiving this error when trying to install Microsoft Unified Communications Managed API4.0: Microsoft Unified Communications Managed API 4.0 i get The hash value is not correct! There is no other instance of Microsoft Unified Communications Managed API installed. Thanks in advance.

Hi 

Have you installed first all features required by exchange 2013, and after installation did you rebooted server ? 

After reboot you should install UCMA 4.0

Also if you have installed any previous versions of UCMA you need to uninstall them using add/remove programs, Then restart server and install UCMA 4.0

Hi,

It might be caused by some uncertainty fator, we recommend install Exchange server in a fresh server.
Would you please download this file and test again?
http://www.microsoft.com/en-us/download/details.aspx?id=34992

Please open setup log file to get more details about this error message, besides, try to restart Windows server then re-install for testing.
If the issue persists, please post setup file without sensitive information for furthershooting.

Thanks