Still unable to reproduce

crawler.fsx

#I "bin/Debug"

#r "FsPickler.dll"
#r "HouseHunter.exe"

open System.Threading
open System.IO

open Nessos.FsPickler
open HouseHunter

let cts = new System.Threading.CancellationTokenSource()
let crawler = new Crawler((fun _ -> async.Zero()), ignore, [ Zoopla.T() ])
Async.Start(crawler.Crawl(0m, 100000m, 0, 100), cancellationToken = cts.Token)

// wait until data is collected
do cts.Cancel()

// just a property that publishes the current crawler state
let state = crawler.State

let fsp = new FsPickler()

let file = __SOURCE_DIRECTORY__ + "/bin/Debug/foo.bin"

using (File.OpenWrite file) (fun fs -> fsp.Serialize(fs, state))

let data = using (File.OpenRead file) (fun fs -> fsp.Deserialize<Map<string, Property>>(fs))

data = state // true