Verified this issue occurs in TDP3.4 to 3.8Beta. TDP3.3 did not have the issue and Toad for Oracle also was fine.
I installed the early release of Microsoft SQL Server 2016 which installed .NET Framework 4.6 which caused the error.
Opened a service request but as soon as they found out I was using a Beta they closed the ticket even though I stated it was not related to the Beta Software.
Service Request # 3144975
Toad Data Point 18.104.22.1681 Oracle connections System.Collections.Generic.KeyNotFoundException
Get this error on every Oracle connection, but it only started after installing “SQL Server Management Studio 2016”. Tried to reinstall TDP22.214.171.1241 but got same error.