webservice call working standalone but not in project

Perhaps you can help me out. I'm making an app to consume a webservice for creditmanagement, using your Web Service Proxy generator. I constructed a proxy with the generator: authoriserproxy.prg. I placed this prg with the other depending prgs/dlls in a new folder authoriserproxy of my main project folder. There are 2 relevant methods: getsaldo and purchase. The getsaldo ("saldo"=balance) method works fine using this code:

(form.init)*** Load the Proxy and Support Class LibrariesDO AuthoriserProxy.prg*** Create an instance of the Proxy
THISFORM.Authoriser = CREATEOBJECT("AuthoriserProxy") && Optionally specify .NET Version
(form.getcard-method - simplified)LOCAL llResult, lnSaldo, lnTransactieID, lnResultCode, lcResultDescription

llResult=.F.
lnSaldo=0
* Saldo ophalen

*** Downloads an object - GetCardData itemLOCAL loItem as GetCardData, lcTransact
lcTransact=GETKEY("Transact")
loItem = THISFORM.Authoriser.GetCard(THISFORM.CardType,THISFORM.Requestor,THISFORM.ClientID,THISFORM.ClientPassword,;
 TRIMSTR(OBJ_NUM(lcTransact)),THISFORM.ClientReference,THISFORM.Pages.Transacties.txtNummer.Value,"",THISFORM.MsgVersion)*** Check for Errors if necessaryIF THISFORM.Authoriser.lError
   THISFORM.Melding("Saldo opvragen mislukt:"+CR+THISFORM.Authoriser.cErrorMsg,"Rood",0)ELSE
   lnTransactieID=THISFORM.Authoriser.oBRIDGE.getproperty(loitem,"transactionid")
   lnResultCode=loItem.ResultCode
   lcResultDescription=loitem.ResultDescriptionIF lnResultCode=0		&& Succes
      lnSaldo=THISFORM.Authoriser.oBRIDGE.getproperty(loitem,"balance")/100
      llResult=.T.ELSE
      THISFORM.Melding("Foutmelding "+TRIMSTR(lnResultCode),"Rood",0) ENDIF

THISFORM.Saldo=lnSaldo

RETURN llResult

As said above code works as expected. So I figured that calling the other method would be simple.

(form.purchase-method - simplified)LOCAL llResult, lnSaldo, lnTransactieID, lnResultCode, lcResultDescription, lnWaarde, loService

lnWaarde=VAL(THISFORM.Pages.Transacties.txtWaarde.Value)*100

loService=THISFORM.Authoriser
llResult=.F.

lnSaldo=THISFORM.Saldo

*** Downloads an object - PurchaseData itemLOCAL loItem as PurchaseData, lcTransact
lcTransact=GETKEY("Transact")
loItem = loService.purchase(THISFORM.CardType,THISFORM.Requestor,THISFORM.ClientID,THISFORM.ClientPassword,;
 TRIMSTR(OBJ_NUM(lcTransact)),THISFORM.ClientReference,THISFORM.Pages.Transacties.txtNummer.Value,"",;
 lnWaarde,THISFORM.MsgVersion)*** Check for Errors if necessaryIF loService.lError
   THISFORM.Melding("Afwaarderen mislukt:"+CR+loService.cErrorMsg,"Rood",0) ELSE
   lnTransactieID=loService.oBRIDGE.getproperty(loitem,"transactionid")
   lnResultCode=loItem.ResultCode
   lcResultDescription=loitem.ResultDescriptionIF lnResultCode=0		&& Succes
      lnSaldo=loService.oBRIDGE.getproperty(loitem,"cardnewbalance")/100
      llResult=.T.ELSE
      THISFORM.Melding("Afwaarderen, foutmelding "+TRIMSTR(lnResultCode),"Rood",0) ENDIFENDIF

THISFORM.Saldo=lnSaldo

RETURN llResult

For the purchase-call however loService.lError returned .T. AND loService.cErrorMsg returned "Methode Authoriser.Authoriser.Purchase is niet gevonden..." (=Method .... not found). I then set a breakpoint to inspect the loService-object and intellisense showed its Purchase-method. So I tried typing the purchase-call directly from the command window and the webservice was called correctly. But after continuing and tracing the loService.purchase()-call in the above code the "invokemethod"-call generated the error I mentioned. strange: what's different from calling it from the Command-window in debug-mode?

And where is this dutch errormsg coming from?

I finally wrote a standalone prg to test the purchase call

(standalone purchase.prg)LPARAMETERS lnValue* SET PATH TO ".\AuthoriserProxy" ADDITIVEDO AuthoriserProxy.prgLOCAL loService, loItem, lnSaldo
loService=CREATEOBJECT("AuthoriserProxy") && Optionally specify .NET Version
loItem = loService.purchase("THECARD","IKKE","MYFIRM","123456",;"Transact1","FM","1234567890123456789","", lnValue*100,"POS")*** Check for Errors if necessaryIF loService.lError
   AppMsg("Afwaarderen mislukt:"+CR+loService.cErrorMsg,"Mislukt","X")ELSE
   lnTransactieID=loService.oBRIDGE.getproperty(loitem,"transactionid")
   lnResultCode=loItem.ResultCode
   lcResultDescription=loitem.ResultDescriptionIF lnResultCode=0		&& Succes
      lnSaldo=loService.oBRIDGE.getproperty(loitem,"cardnewbalance")/100
      llResult=.T.
      AppMsg("Nieuw saldo:"+TRIMSTR(lnSaldo),"Geslaagd","I")ELSE
      AppMsg("Afwaarderen, foutmelding "+TRIMSTR(lnResultCode)),"Mislukt","X")ENDIFENDIF

When I call this program from the Command-window with the command

DO purchase WITH 1

But when I put it in the click()-code of a form-button like:

Purchase(lnWaarde)

Any idea what is causing this behaviour?