Thanks for answering. I resolved. My problem was due to the fact that i was missing a complete Android installation and I was installing only the tools. The problem arose from a fact that I discovered at my expense, that is a bad behaviour of Android sdk Uninstaller, on which I wish to warn other people, hoping that it has been only a problem of mine. Infact I had a previous installation with all my android stuff, b4a included, in a folder c:\android. During my trials, I uninstalled Android sdk by Control Panel. Result is that this uninstaller, which is evidently a mere file delete of all files included in the related folder, i.e. c:\Android in my case, deleted all the content of that folder, included b4a. At first sight I didn't look well not imaginating such thing which generated all my problems. Luckily I have copies of my sources, and also i reinstalled all Android Sdk, but I am now facing another paradox: I cannot download a normal copy of b4a (that I bought, of course). The only admitted download is for the Trial Version, always if I am not wrong again...