#Value error in Excel Public Function

Good Afternoon,

I keep getting the #Value! result using the syntax below. I'm new to writing user defined functions so the solution is not easy for me. Please help.

Public Function FORECAST(SvcDescr, Month1, Month2)
 
If (SvcDescr = "Filter/Block") And (Month2 > 17 Or Month2 <= 29) Then Ret = (29 * 11) + Month1

Else

If (SvcDescr = "Filter/Block") And (Month2 = 17) Then Ret = (17 * 11) + Month1

Else

If (SvcDescr = "Filter/Block") And (Month2 < 17) Then Ret = (12 * 11) + Month1

getFORECAST = Ret

End Function