You will need to install the latest version of WSE RemoteApp in order to correct the issue.

EXPLANATION:

On January 1st, 2016 Microsoft changed the way that digitally signed files are handled in Windows. Before that date, Windows allowed the use of “SHA-1 code signing certificates“. After that date, Windows began enforcing the use of stronger (more secure) “SHA-256 code signing certificates“. For more information see:

Windows Enforcement of Authenticode Code Signing and Timestamping

Due to this change in Windows, we had our existing SHA-1 code signing certificate replaced with a stronger SHA-256 variant. An unfortunate side effect of the replacement process was that our existing SHA-1 code signing certificate was revoked by its issuing certificate authority (effective February 5th, 2016). Which, in turn, caused all files that were digitally signed with our older (and now revoked) SHA-1 code signing certificate to no longer be trusted by our products, causing them to display “An error occurred while validating your license!” (“Cannot validate digital signature!” or “Digital signature not valid!“) error messages.

New versions of our products, that have their files digitally signed with our SHA-256 code signing certificate, have been released (versions 1.232.1232.1232 or greater). Installing the latest release of our products will remove the license validation error messages that you have been experiencing. If you haven’t already done so, you can download and install the latest version from within your server Dashboard.

NOTE: If the “Updates and Support” option on your license has expired, you will need to renew your license in order to be able to install the latest version.

I hope that explains things for you, and I’m sorry for the hassle you’re having on this one.