BEX Problem With WMP

I am a Windows 7 Ultimate 64 Bit User
i have installed K-Lite Mega Codec Pack v.10.8.5

When i try to play SOME – NOT ALL – of my mp4 or mkv files with Windows Media Player i receive the following message:

Problem signature:
Problem Event Name: BEX
Application Name: wmplayer.exe
Application Version: 12.0.7601.17514
Application Timestamp: 4ce7a485
Fault Module Name: vsfilter.dll
Fault Module Version: 3.0.0.304
Fault Module Timestamp: 00000000
Exception Offset: 0012d2ab
Exception Code: c0000417
Exception Data: 00000000
OS Version: 6.1.7601.2.1.0.256.1
Locale ID: 1032
Additional Information 1: 31b0
Additional Information 2: 31b00203ad911f5e36495c07736d6f4d
Additional Information 3: bba9
Additional Information 4: bba91204789e1d41a333807bbe702ec8

Please, if you can, tell me how to fix it

thanks in advance