Validation of ViewState MAC failed

[natedean18]

Hello all, I am working on a DNN website that is version 9.13.8

I am working on a custom implementation of Multi Factor Authentication during the login process. I am using two different panels, one of the username/password fields, and an Update Panel to validate the auth code sent via email.

The first time around the MFA works well, but after logging out and attempting to perform the MFA login again I get the following error:

Uncaught Sys.WebForms.PageRequestManagerServerErrorException: Sys.WebForms.PageRequestManagerServerErrorException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

The panel changes properly, but when trying to validate the token (inserting the code into the textbox and clicking the validate button) the code is not reached and I get the console error above.

I have manually set machine keys and included them in the web config, the site is using its own application pool hosted on IIS, etc.

Any help would be much appreciated. Thanks.