STR problem (*solved*)

[LCD]

Code:

SUB MeineRoutine(x as uinteger,y as uinteger,a$ as string)
IF a$="Test" THEN erg$="Es wurde nur getestet"
ELSE erg$=a$+str(x)+" "+str(y)
end if

PRINT erg$
END SUB

MeineRoutine(30,11,"Hallo")

Compiler claims "temp.bas:48: Error: Undefined label '_MeineRoutine_erg' Errors occured, compilation failed" (No line 48 defined)
I guess, this is a Problem with STR because this:

Code:

dim a as ubyte
a=20
print str(a)

Produces a code that crashes the Emulator

BTW: should POKE STRING adr,string$ work? I mean, if POKE UINTEGER works...