I expect this may be a Vegas issue.

1. Loadup a Video with audio.
2. Ensure there are no pluggin's on the audio track.
3. Press Play (important that it is playing, idle it doesn't produce the exception)
4. Add and then delete the pluggin on the audio track so that the track pluggin window stays open although is empty.

5. Select the "add" pluggin (little green thing) on the track and add LinMB

6. Press "OK" and you should get the following exception (error file below picture)

Sony Vegas 5.0
Version 5.0a (Build 134)
Exception 0xC0000005 (access violation) READ:0x4 IP:0x41F491
In Module 'vegas50.exe' at Address 0x400000 + 0x1F491
Thread: GUI ID=0x8C0 Stack=0x12F000-0x130000
Registers:
EAX=0bc1b4e0 CS=001b EIP=0041f491 EFLGS=00010206
EBX=00000000 SS=0023 ESP=0012f3f0 EBP=00000000
ECX=00000000 DS=0023 ESI=0bc23880 FS=003b
EDX=00000003 ES=0023 EDI=0bc23880 GS=0000
Bytes at CS:EIP:
0041F491: 8B 51 04 33 DB 33 C0 83 .Q.3.3..
0041F499: FA 02 0F 85 24 02 00 00 ......
Stack Dump:
0012F3F0: 0BC3CB58 0BAC0000 + 17CB58
0012F3F4: 0BC23880 0BAC0000 + 163880
0012F3F8: 00000000
0012F3FC: 00000000
0012F400: 00000000
0012F404: 00000000
0012F408: 00000000
0012F40C: 00000000
0012F410: 00000000
0012F414: 00000000
0012F418: 00424151 00400000 + 24151 (vegas50.exe)
0012F41C: 0BC23880 0BAC0000 + 163880
0012F420: 0BC1B4E0 0BAC0000 + 15B4E0
0012F424: 0BC23880 0BAC0000 + 163880
0012F428: 0012F8E0 00030000 + FF8E0
0012F42C: 00000000
> 0012F444: 006C0050 00400000 + 2C0050 (vegas50.exe)
> 0012F448: 00670075 00400000 + 270075 (vegas50.exe)
> 0012F44C: 0049002D 00400000 + 9002D (vegas50.exe)
0012F450: 0020006E 00140000 + C006E
> 0012F454: 00680043 00400000 + 280043 (vegas50.exe)
> 0012F458: 006F006F 00400000 + 2F006F (vegas50.exe)
- - -
0012FFF0: 00000000
0012FFF4: 00000000
0012FFF8: 007287E0 00400000 + 3287E0 (vegas50.exe)
0012FFFC: 00000000