To correct this problem there is a bit annoying procedure.
1) download virtualdub (it's free)
2) load the first avi segment, and go to menu Video --> Direct stream copy
3) Go to menu audio and select "No audio"
4) press F7 and save the video only segment
5) Press CTRL-W to close the avi.
6) Open again the same avi segment and go to menu File --> Save Wav
7) Remember where you are saving that file, because you need it again later.
8) Repeat the same things for the second AVI segment, so you will have again a video and an audio file for that segment.
9) open the first avi with no audio
10) go to menu Audio --> Wav file
11) Select the corresponding wav file you previously saved on hard disc
12) Go to menu Audio and select "Full processing mode"
13) Go to menu Audio and select "Compression"
14) Select a compressing codec, for example MP3, selecting the bitrate you like
15) Go to menu Video and select "Direct stream copy"
16) Press F7 and save the first segment with audio on another folder.
17) Repeat the same procedure with the second segment, being careful to select the same compression parameters of the audio part.
Finally, when you have two segments with the audio part encoded in the same way, you can use again virtualdub to join these segments, with the following procedure:
18) Open the first AVI segment
19) Go to menu File --> Append avi segment
20) Select the second segment
21) Go to menu Video and select "Direct stream copy"
22) Go to menu Audio and select "Direct stream copy"
23 Press F7 and save the joined avi in a folder you like.
I hope to have not forgot a step :doh: