Flash may freeze due to the following reasons.
Symptom 1: The Flash froze the moment you "Allowed" camera access.
If this is the case, the devices connected to the computer or the desktop capture soft may be causing the problem. Please turn of the said devices on the device manager or unplug the device from the computer to identify the problem.
Symptom 2: The screen becomes green-ish and the image shown in Flash freezes.
If this is the case, the GPU assisted video playing function on Flash 10.1 may have caused the problem. Please take the following steps to turn off the GPU assisted video playing function.
Right click on top of the Flash and click on "Settings".
Once the AdobeFlashPlayer settings is displayed, check-off the "Enable Hardware Acceleration"
Symptom 3 : Others
In regards to the trouble that occurs after acquiring the program block for broadcast please try out the following solution.
(1) Browser Compatibility
If you are using Internet Explorer, please use another browser such as FireFox.
(2) Compatibility problem in the Flash version
Certain version of Flash may cause the player to freeze.
If this is the case, please another version of flash or use another browser.
*Install the latest version from here.
(3) Delete the "Website Memory Area" in Flash
If there is something wrong in "Website Memory Area" in Flash it may cause the player to freeze.
Please try deleting the "Visited Websites" for "live.niconico.com".
(4) Compatibility Problem with the desktop capture software
If you are using a particular desktop capture software, the Flash and video streaming software may freeze due to video image with abnormal bit rates being sent.
If this is the case please uninstall the software.
(5) Compatibility problem with the video effect software
If you have a software that adds effects to the videos installed from a CD that came with a camera please uninstall them.
If this does not solve the problem, please reinstall the camera driver.
(6) Problem with Adobe Flash Player
After logging out from niconico.com, reboot your computer.
If the steps above does not solve the problem, there may be a problem between your computer environment and the Adobe Flash Player. If possible please reinstall the OS and contact Adobe Flash Player about the forced termination.