Why does the error "the type or namespace name 'syncfusion' could not be found(are you missing a using directive or an assemble reference)" occur?

The error “type or namespace name ‘Syncfusion’ could not be found (are you missing a using directive or an assembly reference?)” occurs due to the following reasons: 

1. Referring the application’s reference DLLs like the DLL version as Target Framework version. 

• TargetFramework version is lower than Syncfusion DLL’s version 

Example: 

TargetFramwork version: 3.5 

Syncfusion Installed framework version: 4.6

2. Creating application under one .NET Framework. 

• You can use multiple projects for your application. In every application, referred Syncfusion DLLs version should be the same. 

3. The GAC assemblies are removed or reference path differs from the Target Framework. 

• Trying to refer the higher version DLLs in lower framework version projects.

4. Mismatching assemblies of GAC assemblies and user defined reference path assemblies. 

• You can see this by opening your project in notepad or unloading and editing your project in Visual Studio. Syncfusion assemblies should not be as illustrated in the following screenshot.
• So, remove the hint path and assembly settings like as below illustrated screenshot