Error:- 500 Internal Error
Description:- This error comes only for subsites and subsite administrators can browse the subsite without any issues. The parent site collection is also browsable without any issues. Only member or visitors of the subsite get the error "500 Internal Error"
1. Go to the subsite settings page by adding /_layouts/settings.aspx at the end.
2. Select Advanced permissions -> Settings -> Permissions Level
3. Click "Edit Permissions level"
4. Click "Inherit Permissions from parent"
Now the subsite should be browsable by all without any issues.