SendMail input string not in the form for an e-mail address

Hello everyone,

We recently made the jump from version 7 to 9, and a rule that was previously working is now throwing an error. We are trying to use the BRApi.Utilities.SendMail functionality after a certification is done through the DataQualityEventHandler, but OS is giving us the following message when executing the certification

The specified string is not in the form required for an e-mail address.

We verified the toEmailAddresses parameter is a List(Of String) with a single item in the format "user@mail.com". What can be causing this issue?