What is your connection method ?
avast checks for updates when a connection is found so if say you were using dial-up once you connect avast will check for updates, this may take a little time. If you then disconnect avast won't be able to update and it will cycle through the different servers in the servers.def file trying to connect but won't be able since the original connection has been closed.
Eventually when it gets to the end of the list it will pop-up the red failed to update, you click that and it gives more information, this may be the second pop-up you mentioned.
You can dictate how avast updates, see the Program Settings, Update, (Basic).