Why am I receiving exception from Office's Outlook library?

Question

I have an application that calls

Email hello = new Email(appropriate constructor);
hello.Email_Send();

I\'m receiving the exception:

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Answer 1

I ran into the same issue, and as previously said: if Visual Studio is running as Administrator then Outlook prevents another instance with a different user. My VS solution is starting several projects, and I need it to run as Administrator, so what I did is run Outlook as administrator while debugging. This solved my problem.

Answer 2

This error was caused by visual studio being run as admin. Outlook doesn't allow separate users to access the same mailbox (I had the outlook application open on desktop). Even though I have local admin access w/ my domain user, running VS as admin must associate the process to a different user object? Not exactly sure how this works, but... Resolved.