This alert is related to a security feature added in TMSPS 3.3 Patch 3, which lets the SPS determine whether the AU source is legitimate and trustworthy by validating the signature files during pattern update process.

Sometimes, there are chances where the Active Update team (responsible for the Active Update server, where the pattern updates are published) is unable to provide the latest signature file along with the pattern file itself. This causes the validation process to fail. Once it fails the pattern update process stops and will show that particular error message.

This is also recorded in the "Known Issues" section in the TMSPS 3.3 Patch 3 Readme and, at the moment, the workaround is to set the pattern update to every 15 minutes. This is based on letting the pattern update process having a higher chance of success due to the more frequent updates because the validation error blocking the pattern update does not happen every time.

Another option is to completely disable this feature. However, by disabling this feature, there will be no way for the SPS to validate the AU source. If this is acceptable to you and you wish to disable it, please follow these steps:

a) Log in to SPS via SSH using your root credentials.
b) Edit the file /var/tmcss/conf/AU.ini
c) Find the key CheckSignature and change the value from 1 to 0.