Thank you. Unfortunately, I didn't receive notice that you had replied. Support provided some suggestions that didn't work. I was finally able to resolve this by renaming the folder C:\ProgramData\Veeam\Backup365\ConfigDB to ConfigDB.old and C:\ProgramData\Veeam\Backup365\ProxyDb to ProxyDb.old as well as renaming C:\ProgramData\Veeam\Backup365\Config.xml to Config.xmlold and C:\Programdata\Veeam\Backup3656\Proxy.xml to Proxy.xmlold. I also renamed the registry key HK_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Backup for Microsoft Office 365 to OldVeeam Backup for Microsoft Office 365, exported the registry key HKLM\SYSTEM\CurrentControlSet\Services\Veeam.Archiver.Proxy then deleted it. After rebooting the server, I was able to install Veeam Backup for Office 365 1.5.