Debugger crash with event BEX in StackHash (Unity 3)

Mono debugger crashes while stepping in code. I am working on a Windows platform so the "debug" dialog appears. Title: "Unity Editor has stopped working"...normal crash window. Problem details shown below.

The crash happens when expanding and viewing local variables. In particular, I'm looking at the contents of a GameObject. The local window shows a few of the fields as "evaluating..."

My environment: Windows7, 64 bit OS Unity 3.0.0f5 (pro license) Mono 2.4

One potential issue - I am using a DLL reference in the project. The DLL is from code written in C# and was built in Visual Studio (version 2008). I am using the reference directly, in other words, it is not native code and is not a DLLImport.

Problem details:

Problem signature: Problem Event Name: BEX Application Name: Unity.exe Application Version: 3.0.0.51258 Application Timestamp: 4c9f87e1 Fault Module Name: StackHash_e98d Fault Module Version: 0.0.0.0 Fault Module Timestamp: 00000000 Exception Offset: 00000000 Exception Code: c0000005 Exception Data: 00000008 OS Version: 6.1.7600.2.0.0.256.4 Locale ID: 1033 Additional Information 1: e98d Additional Information 2: e98dfca8bcf81bc1740adb135579ad53 Additional Information 3: 6eab Additional Information 4: 6eabdd9e0dc94904be3b39a1c0583635