Option strict basically disallows any implicit conversions of data types. The reason for this, is that somewhere down the line (usually after youve already deployed the application), converting one type to another type might cause undesired results and hence, crashing your application. So with Option Strict On, you are not allowed to build your solution/project if you have implicit conversions. Try using CType(STRING, INT) or vice-versa, so you arent implicitly converting data types.