I was also experiencing the same issue.
When I debug the Action and look at the ModelState.Values[1].Errors[0].Exception for example, I see the following:
{“The parameter conversion from type ‘System.String’ to type ‘System.Collections.Generic.KeyValuePair`2[[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Int64, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]’ failed because no type converter can convert between these types.”} System.Exception {System.InvalidOperationException}
In my scenario, my SelectList is created from a Dictionary and i use this in my view:
<%=Html.DropDownListFor(x => x.MyDictionary,
new SelectList(
Model.MyDictionary,
"Value",
"Key")) %>
When I changed it to:
<%=Html.DropDownListFor(x => x.MyDictionary.Keys, // <-- changed to .Keys
new SelectList(
Model.MyDictionary,
"Value",
"Key")) %>
It worked without issues.
Thank you.