Cannot obtain value because it has been optimized away

Question

I have a problem with debugging... All of a sudden I can't see the values of most variables while debugging. I've managed to get two different messages in the Immediate Window:

Cannot obtain value of local or argument 'parameter' as it is not available at this instruction pointer, possibly because it has been optimized away.

and

Internal error in the expression evaluator.

I've tried and checked the following things:

1. Solution Configuration is set to debug (not release)
2. Project -> Settings -> Build -> Optimize code is not set
3. Tools -> Options -> Debugging -> Use Managaed Compatibility Mode (didn't work)

Do you have any further ideas how I can properly debug again? :(

Thanks in advance

Edit The code is nothing special.. it happens when I try to watch what's inside parameter[Key]

public void AddOrUpdateQuartzJob(string jobName, IList<KeyValuePair<string, string>> parameters)
    {
        var jobDetail = this.GetJobDetail(jobName);

        if (jobDetail != null)
        {
            foreach (var parameter in parameters)
            {
                jobDetail.JobDataMap[parameter.Key] = parameter.Value;
            }
        }
        else
        {
            this.ScheduleNewJob(jobName, parameters);
        }
    }

Answer 1

The best way I've found to convince the JIT compiler not to optimize the code is to use an INI file with the name of the assembly in the same folder the assembly is in with the contents:

[.NET Framework Debugging Control]
GenerateTrackingInfo=1
AllowOptimize=0

Note that it has to be the name of the assembly, not the name of the process EXE (unless it is the EXE assembly you want to debug). E.g. if you have an assembly MyCode.dll the INI file name would be MyCode.ini.

Here are some slides from a presentation on .Net debugging which show the difference:

With Optimization:

Without Optimization: