I get this when I click (not double click) on a AC3 file in explorer tab.

Sony Vegas 4.0
Version 4.0e (Build 239)
Exception 0xC0000005 (access violation) WRITE:0xA49D080 IP:0x8A09B6B
In Module 'mpegin.DLL' at Address 0x89F0000 + 0x19B6B
Thread: GUI ID=0xAD8 Stack=0x118000-0x130000
Registers:
EAX=00000000 CS=001b EIP=08a09b6b EFLGS=00010246
EBX=0011a10c SS=0023 ESP=00118b88 EBP=fffffe83
ECX=00000008 DS=0023 ESI=00118bd8 FS=003b
EDX=04a45cc8 ES=0023 EDI=0a49d080 GS=0000
Bytes at CS:EIP:
08A09B6B: F3 A5 5F 5E 5D 5B C3 90 .._^][..
08A09B73: 90 90 90 90 90 90 90 90 ........
Stack Dump:
00118B88: 00000000
00118B8C: 0011A10C 00030000 + EA10C
00118B90: 00000003
00118B94: 00000200
00118B98: 08A0B81E 089F0000 + 1B81E (mpegin.DLL)
00118B9C: 0011A10C 00030000 + EA10C
00118BA0: FFFFFE83
00118BA4: 00118BD8 00030000 + E8BD8
00118BA8: BFF00000
00118BAC: FFFFFFFF
00118BB0: 0011A10C 00030000 + EA10C
00118BB4: 00000000
00118BB8: 000001B6
00118BBC: 00000001
00118BC0: FFFFFDFF
00118BC4: 00000200
> 00118BE0: 00830701 00400000 + 430701 (vegas40.exe)
00118BE4: FFFFFDFF
00118BE8: 00000003
00118BEC: FFFFFE83
00118BF0: E949105A
> 00118BF8: 08A02D4F 089F0000 + 12D4F (mpegin.DLL)
00118BFC: 00000001
> 00118C00: 08A95FFC 089F0000 + A5FFC (mpegin.DLL)
> 00118C04: 77E61BEA 77E60000 + 1BEA (kernel32.dll)
00118C08: 0011A10C 00030000 + EA10C
> 00118C0C: 77C43B00 77C10000 + 33B00 (msvcrt.dll)
00118C10: 6D5C3A64
> 00118CD0: 77C37BBE 77C10000 + 27BBE (msvcrt.dll)
> 00118CE0: 77C4247B 77C10000 + 3247B (msvcrt.dll)
> 00118CF8: 77C5A7A0 77C10000 + 4A7A0 (msvcrt.dll)
> 00118D14: 08A028E2 089F0000 + 128E2 (mpegin.DLL)
00118D18: 0011A10C 00030000 + EA10C