Sometimes, while working in MS.NET you add the reference of the project or the assembly and when you build the solution you still get the following errors:
1. Error 507 Metadata file '..\bin\Debug\YYY.dll' could not be found.
2. Error 74 The type or namespace name 'XXX' does not exist in the namespace 'YYY' (are you missing an assembly reference?).
So just to avoid a lot of scratching your heads, the issue involved here is the mismatch of the target framework property of the dll or project for which the reference has been added:
Solution: Select the project and Go to property page. On "Application" tab select the "Target Framework" as set in the calling project as shown in screenshot below:
1. Error 507 Metadata file '..\bin\Debug\YYY.dll' could not be found.
2. Error 74 The type or namespace name 'XXX' does not exist in the namespace 'YYY' (are you missing an assembly reference?).
Solution: Select the project and Go to property page. On "Application" tab select the "Target Framework" as set in the calling project as shown in screenshot below: