This error message is produced by Outlook Manipulator when the software cannot point at the right account to create a MAPI profile. This can happen for a few reasons, for example you have multiple mailboxes with the same or similar mailbox aliases, primary SMTP addresses, mailbox display names or the latter do not match accounts' samAccountName AD property (users logon names). This is a known issue to Microsoft and even other software vendors.
Please verify the current naming structure ensures all users have a unique alias. This would mean no user's alias can be a substring of another. This will avoid ambiguous lookup results.
Assume you have these two users in your organization Alice Smith (asmith) and Anthony Smithson (asmithson)
A lookup for user Alice Smith (asmith) would return MAPI_E_AMBIGUOUS_RECIP because asmith is a substring of asmithson. However if the search is reversed there would be no error returned.