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We can't know. you are not offering any system information, info about your source files, your comp settings or what version of AE you are using even. This si not going to yield any useful responses.
It appears that Microsoft has issued the fixed update:
See the "Update FAQ" section:
"Why was this bulletin revised on August 13, 2013?
Microsoft revised this bulletin to rerelease the 2803821 update for Windows 7 and Windows Server 2008 R2.
The rereleased update addresses an application compatibility issue in which WMV encoded video could fail to properly render during playback. Windows 7 and Windows Server 2008 R2 customers should install the rereleased update."