ASPNetCore - ValidationSummary does not contain a definition for ValidationSummary

Error : 'ValidationSummary' does not contain a definition for 'ValidationSummary'

This is because the namespace that includes ValidationSummary is already included. 

Solution : All you have to do is delete the part that says Validation summary.

eg: asp-validation-summary=”ValidationSummary.ModelOnly” would be asp-validation-summary=”ModelOnly”.

Happy Coding NetCore :)