Try quitting WireTap Pro and deleting "com.ambrosiasw.wiretap_pro.plist" from your ~/Library/Preferences folder. Then reinstall WireTap Pro. You can download the final version of WireTap Pro,1.3.4, from:
Please note that WireTap Pro was discontinued 2 years ago and is no longer sold or supported. It is also not compatible with 10.5.7 or later. Please see the FAQ for a workaround.