I have a client with a new Panasonic camcorder and we encountered this same problem. It records .asf files, but Windows Media Player (version 9 or 10) gives the "Windows has blocked this software" message, referring to sg726acm.cab. I tried this on several XP machines, including mine which has the K-Lite codec pack. KiLite is NOT the solution here, which surprised me. Changing Windows security settings also makes no difference.

I have Googled around for a solution, and this forum is absolutely the only place I found a discussion of this problem. Maybe the Panasonic SV-AV100 is too new for complaints to be registered.

Actually, the solution can be found in this thread. You need to download
http://codecs.microsoft.com/codecs/i386/sg726acm.cab, unpack it, then right-click on the .inf file to install it.

My client is returning his new camera because he needs to be able to make CDs to give to his customers, and we can't expect them to follow these convoluted instructions to make the files play. This is a major PITA.