Why we need to delete WAS window's service?

By default, when installing WebSphere 6.1, it is selected to start as windows services (unlike WebSphere 6.0, you can choose manual startup during the install). By having WebSphere start as a Windows services (starts up WebSphere when Windows starts) can cause various problems. Some of them are 1) WebSphere CE server will not start properly if WebSphere is started before DC is up and running, this is usually a problem for environment with Tivoli DS since Tivoli DS require a longer time to start. 2) WebSphere server will not start up/shut down if the WASService.exe is corrupted

the message stating that WASServices.exe is not a valid WIN32 application and your WASService.exe file is 0K (this probably means that your WASServices.exe file is corrupted), you need to copy the WASService.exe from other WebSphere 6.1 server and then execute the WASService.exe -remove command again to remove it. Please note that by doing so will enable you to start WebSphere server again, but it is not guarantee that your server is clean. The proper way to reghost or rebuild your WebSphere 6.1 server.