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Welcome to the forums, vinomother
What Avast is trying to tell you with those pop-ups is that one day soon, v4.8 will no longer be supported and that will happen before April, 2011. So, you should not wait and loose the registered time you already have. Because, the end for v4.8 may end tomorrow, or next Monday, or on Dec 27th, or ...... the real end is not known but it will certainly occur very soon.
Avast does not want you to be using v4.8 when the end of support comes as you will then be using out of date definitions and will not be well protected. Avast wants you to update to v5.0 so that you will continue to be well protected. Please follow the advice of the pop-ups as well as the advice above.
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