Toad has an error logging component called EurakaLog. EurekaLog and Dynatrace both hook into the CreateFileA WinAPI function. The problem is that EurkaLog wasn't counting on another app hooking into the same function, and it EurekaLog's hook fails because DynaTrace has already hooked it.
We'll have this fixed soon in beta after 14.0 is released. We actually have the fix from EurekaLog already, but it was too late to include in Toad 14.0.
Toad 14.0 will at least have a nice dialog when this error happens explaining what it means, causes, and solutions.
As I said, you can use a 32 bit Toad to work around it with Toad 13.3. But if you do that, you'll also need to install a 32 bit Oracle client on that machine.