help with avi to mpeg in virtual dub please!!!

[kilika]

hi i am new to converstion so i hope i don't sound dumb

i am converting a large mpeg1 file to avi with virtual dub

the settings i use are divx 5.02 (460) and lame mp3 12000 96kbs

when the file is done it plays fine until i try to move forward in the film and i can hear the sound but not see the picture.
can any one help
have i used the wrong settings

thx in advance kilika

[wee haggis]

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