(1) I don't use either of these third party apps, but first, get your software up to date.
Use your MBP's Disk Utility to repair permissions. Then download and apply the latest Combo Update. Currently, the latest Snow Leopard Combo is here: http://support.apple.com/kb/DL1399
Repair permissions again immediately following the system restart that completes the Combo update.
Then verify that you are using the latest versions of CamTwist and BlogTV that are compatible with your 10.6.8 system.
Repair permissions again after applying any other needed software updates.
(2) If your problem persists after the updates, I suggest that you next verify that your problem is NOT related to your MBP's camera. Test your MBP's camera with more than on of Apple's camera enabled apps using the suggestions from the article: http://support.apple.com/kb/HT2090
Be sure to check more than one Apple camera-enabled app in more than one user account. However, don't use a "Guest" account for testing. If your Mac only has one account, create a new user account for testing.
(3) If your camera works with all Apple's apps in all user accounts you test, then your problem is with your third-party apps.
CamTwist also offers a broad range of Help options including its own dedicated Support Forum. The CamTwist users who post there may have already found the answers to your problem.
Start by looking for help with the one that gives you the most trouble. If they both work properly when used alone but only give trouble with you try to use them together, you will need to search both sites for help using each with the app.
(4) If you'd rather try more things on your own first, check out this YouTube presentation about using Camtwist with BlogTV. If that doesn't help, you can also search for other CamTwist BlogTV help in both web pages as well as YouTube.