If after installing Giftcert extension you are getting issues with paypal payments, you most likely have a license problem.
Most often the problem is that you are missing IonCube loader. Make sure that when reviewing your PHP information you can find IonCube extension loaded.
Another common problem is misplaced license file. Please check that you can find ugiftcert.lic.txt file in app/ folder or if you use compilation, in Magento site root folder.
Last problem is wrong license file. Please make sure that your license file supports the setup you use it on (domain name, IP address, MAC address)
If all of the above are in place and working, contact us on email@example.com, and provide your site address and FTP write access.