Dear Pranjala Jayaramegowda,
Wage type model is a part of the payroll configuration maintained in the Personnel Administration->Payroll>Basic Pay>Wage Types>
Revise Default Wage Types
Here in the view V_T539A the wage type model is maintained. This consists of a list of wage types (ideally not exceeding 20 wage types) maintained for a particular wage type model that would be defaulted using feature LGMST in the Basic Pay Infotype 0008.
Your wage type model has changed on 01/04/2014 and you are trying to create a basic pay record with this date in between your start and end date of record creation which is the reason you are probably getting the error.
Ur's
Mohan