SAPWR error message: RFC user is defined in a particular client, e.g. 800
Now,  while launching SAP, GuiXT responds with an error message because the user and password are not defined in client 000. Is there a way to suppress this error message that pops up on initial logon?

Yes, as of version GuiXT 2003 Q3 4 GuiXT suppresses this error message  when you use the "RFC current client" option in profile. Alternatively, you can use the notation "SAPWR,client=800". The logon script is then read as well.

See also the documentation Location of GuiXT profile