Generic Extractors and InfoPackages

I have created a Generic extractor and have replicated it to BW. The extractor has been Delta enabled using the Timestamp and choosing one of the key fields Equipment No. When I create an InfoPackage (Init) I get a popup box with the message ‘There is no active delta initialization for this IS/QS/DATA source. It is able to carry out the load and I am also able to load a delta package. What does the message mean and could I face problems? Thanks