bad dll calling convention

[ejudy]

here is C function:

int Dosth (char inflag)

here is calling from VB:

public declare function Dosth lib "**.dll" (byval flag as byte) as long

dim a as byte
dim ret as long
ret=Dosth(a)

when I call Dosth, got "bad dll calling convention"..... is it because the dll itself(it is now a try version dll) or my vb code?

Thanks if you can answer.