Unable to evaluate expression because the code is optimized or a native frame is on top of the call stack

Make second argument of Response false as shown below.

Response.Redirect(url,false);

In a bug I was investigating there was a Response.Redirect() and it was executing in an unexpected location (read: inappropriate location - inside a member property getter method).

If you're debugging a problem and experience the "Unable to evaluate expression..." exception:

1. Perform a search for Response.Redirect() and either make the second parameter endResponse = false, or
2. Temporarily disable the redirect call.

This was frustrating as it would appear to execute the Redirect call before the "step through" on the debugger had reached that location.

Use this, works for me always.

Response.Redirect(Request.RawUrl, false);

Here, Response.Redirect(Request.RawUrl) simply redirects to the url of the current context, while the second parameter "false" indicates to either endResponse or not.

This problem may be a result when you have a razor page in mvc with a model that has some validation rules. When you post from a form and you forget to display validation errors on some field, then this message might come up. Speculation: this could be if the method you are posting to is different and used by other sources or resides in a different place than the method serving the original request.

So because it's different, it can't return to the original page to display or handle the errors because the excecution and model state is not the same (something like that).

It can be slightly difficult to discover, but easy mistake to do. Make sure your recieving method actually validates all possible ways to post to it.

for instance, even if you have serverside validation that actually makes it impossible to write in the form a string that is bigger than the max allowed by your validation, there could be other ways and sources that post to the recieving method.