You have probably entered an incorrect serial number/installation code during the installation of the program. Uninstall BatSound and then install it again. The serial number is printed on a label on the inner back cover of the BatSound user's manual. Please note that the serial number is case sensitive.
Yes, from BatSound version 4.1 it is possible to run the program from other accounts, as long as the program was installed on that particular computer.
This occasionally occurs in Windows Vista and 7 when the chosen Sound Device has been set to "listen mode". To check and change this, open the Recording devices window (e.g. by right-clicking on the loudspeaker icon in the lower right corner of the screen). Select the recording device that you are using and select Properties. In the Listen tab, make sure that "Listen to this device" is left unchecked.