We have some custom forms in SharePoint site and only with the full control, users able to access those forms, otherwise, they are getting
this site has not been shared with youerror.
When I checked log I am seeing the error
System.Runtime.InteropServices.COMException: The user does not exist or is not unique., StackTrace: at Microsoft.SharePoint.SPUser.InitMember() at Microsoft.SharePoint.SPUser..ctor(SPWeb web, SPSecurableObject scope, String strIdentifier, Object[,] arrUsersData, UInt32 index, Int32 iByParamId, String strByParamSID, String strByParamEmail, SPUserCollectionType userCollectionType, SPUserCollectionFlags ucf, Boolean isSiteAuditor) at Microsoft.SharePoint.SPUserCollection.GetByLoginNoThrow(String loginName, SPUserCollectionFlags ucf) at Microsoft.SharePoint.SPWeb.EnsureUser(String logonName)...
When I checked using my login, even without full control I am able to see and submit the forms.