Can't join two avi files with virtual dub 1.9.10

I downl. the taking of pelham 123 and when i try to join the two parts avi into a single part it doesn't work,

when i save as the file all it is saving is an 11kb file.

Also when i open the first part the program tells me:
"truncated or invalid compressed audio format detected (18 bytes shoud be 36)Attempting to fix"

What can i do?

 

Try joining with AviDemux.