We have changed one of our scripts and now get an RFC error message
RFC_ERROR_SYSTEM_FAILURE for the function module BAPI_USER_GET_DETAIL
("invalid user name or password"). We are not using the "Call" statement. What could be the reason for the RFC error message?
In your script, you are probably using one of the following options:

if Q[Role=...

or

InputField .... -date

or

Set ... decimalseparator=UserDefault

For these options GuiXT needs to read the user configuration via the function module BAPI_USER_GET_DETAIL. Please enter a valid RFC user and password in GuiXT profile. Concerning the password, please observe that you have to either user only uppercase letters or, if not, enclose the password in inverted commas, e.g. RfcPassword "bdMIh49$".