strange out-of-memory exception during serialization

Question

I am using VSTS2008 + C# + .Net 3.5 to run this console application on x64 Server 2003 Enterprise with 12G physical memory.

Here is my code, and I find when executin

Answer 1

1) The OS is x64, but is the app x64 (or anycpu)? If not, it is capped at 2Gb.

2) Does this happen 'early on', or after the app has been running for some time (i.e. n serializations later)? Could it maybe be a result of large object heap fragmentation...?