Issue #2: MS Outlook (2016) Error: Additional MS Exchange Server Accounts cannot be added......

Add two Reg keys:

• HKEY_CURRENT_USER\Software\Policies\Microsoft\Exchange\ 
• HKEY_CURRENT_USER\Software\Microsoft\Exchange\
  (These might not exist - you may have to create them.)
  
  

Then add a new DWORD to each: MaxNumExchange
(Add a DWORD; do NOT add a new QWORD. QWORD did not work for me.)

Then modify the new DWORDs.
(I gave each a value of 30.)