Error: Type <customtype> cannot be resolved when placing a widget on the page

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EnvironmentProduct: Sitefinity
Versions: 5.x, 6.x, 7.x, 8.x, 9.x
OS: All supported OS versions
Database: All supported Microsoft SQL Server versions
Question/Problem Description
The exception "Type <custom type> cannot be resolved" is thrown. The type in question is a custom control in Sitefinity that is registered in the Toolboxes. The control type cannot be found in the assembly.
Steps to Reproduce
Clarifying Information
Error MessageType : System.ArgumentException, mscorlib, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089
Message : Type "SitefinityWebApp.Widgets.MyWidget, SitefinityWebApp" cannot be resolved.
Source : Telerik.Sitefinity.Utilities
Help link :
ParamName :
Data : System.Collections.ListDictionaryInternal
TargetSite : System.Type GetType(System.String, Boolean, Boolean)
HResult : -2147024809
Stack Trace : at Telerik.Sitefinity.Utilities.TypeConverters.TypeResolutionService.GetType(String name, Boolean throwOnError, Boolean ignoreCase)
at Telerik.Sitefinity.Utilities.TypeConverters.TypeResolutionService.GetType(String name)
Defect/Enhancement Number
The control type or namespace has been changed or does not exist in the project anymore. The control might not be compiled in the Sitefinity Web App assembly if it is not included in the project.
Ensure the control namespace and assembly are correct. Use the exception message. For example:
"Type "SitefinityWebApp.Widgets.MyWidget, SitefinityWebApp" cannot be resolved."
Verify that there is a control MyWidget and its namespace is SitefinityWebApp.Widgets and it is in the SitefinityWebApp project.

Ensure the control is included in the project and if not, then include it by right-clicking the file and selecting "Include in project". 

Include in the Project

Build the project to compile the control in the assembly.

If the control type name or namespace has been changed, set the correct ones in the Toolbox: Go to Advanced settings -> Toolboxes -> Toolboxes -> PageControls -> Sections, find the section of the control -> Tools, select the control and edit its Type.
Last Modified Date3/6/2017 7:09 AM

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