HchangePassword problem (no replies)

Hello to you all,

I have multiple files that are used and I want to password protect them.
There are two possibilities:
a) The file is already password protected
b) It is not passwordprotected

I don't know which customers files are already protected. So I thought:
HPass(MyFile,"Mypassword")
HChangePassword(MyFile,"Mypassword") // changing it to the same password in case of b)

a) this code works fine
b) the HPass and HChangePassword gives a result: true. But it is not password protected afterwards???

In case off b) : When I leave the HPass away then it encrypts but I need it when it is encrypted.
It seams that HChangePassword does not work when I use a HPass before it when the file is not password protected.
Any ideas on how to solve this?