User field is not updated thru API call

Hello!

We are using Clarizen API to synch projects attributes (user fields) with our accounting system, and for several (out of hundreds that are updated OK) projects we are getting errors back from API call - see the request and response details @ https://www.screencast.com/t/fiOrzkDf1l2

We tried to compare data between the projects where user field updates OK and the projects where it fails and do not see any difference in data, so it could be something is wrong with API or with internal (not UI/API exposed?) data values for affected project.

For Clarizen's R&D staff - project id = 17w8765s4tb9q8bg6ouegs25f5431, direct link https://app2.clarizen.com/Clarizen/Project/5847504257, the field we are failing to update is "B1: BH Open Qty"

Let us know if you need another instances of affected projects.

The code we use:

    private class ProjectRecord
    {
        public string Id { get; set; }
        public string CardCode { get; set; }
        public decimal? Balance { get; set; }
    }

    public static class ClarizenTypes
    {
        public const string Project = "Project";
    }

...

...

        private static List<BaseMessage> BuildApiUpdateMessages(List<ProjectRecord> projects, Dictionary<string, decimal> balances)
        {
            var rez = new List<BaseMessage>(projects.Count);
            foreach (var project in projects)
            {
                decimal balance;
                if (balances.TryGetValue(project.CardCode, out balance))
                {
                    if (balance != project.Balance)
                    {
                        rez.Add(new UpdateMessage
                        {
                            Entity = new GenericEntity
                            {
                                Id = new EntityId {TypeName = ClarizenTypes.Project, Value = project.Id},
                                Values = new[] {new FieldValue {FieldName = "C_B1_OpenBH", Value = balance}}
                            }
                        });
                    }
                }
            }
            return rez;
        }

* project.Id never equals to null

* BaseMessage, UpdateMessage, GenericEntity, EntityId, FieldValue are defined in https://api.clarizen.com/v1.0/Clarizen.svc 

* Output of the function is pushed to http://clarizen.com/api/IClarizen/Executemethod 

Thanks in advance!