First, use the latest version. If the customer is not using the latest version, then stop everything, update your app to use the latest version of TurboActivate, and then try again.
https://wyday.com/limelm/help/faq/#latest-libs
If (*only after updating to the latest version*) the customer is still getting the error we have a full description of the way to debug it in TurboActivate.h. Again, see the latest version.