System Information
Windows 8.0
Intel HD 4600

Blender Version
Broken: 2.73.6 12ed439
Worked: Before new proxy set up

Short description of error

setting proxies without enabling them crashes blender
Exact steps for others to reproduce the error

1. Open VSE
2. And a strip (I used Movie Strip)
3. Set proxies to 25%
4. Hit ok

Crash file only gives the leading to events but not the last so no help there

Here it is anyway though