Ada string concatenation

I keep on getting CONSTRAINT_ERROR from the string concatenation code below:

for Line in 1 .. 5 loop
Fault_Data.Lru_Label := "Fault 0" & Integer'Image (Line);
...
end loop;

The link below shed light on how to do string concatenation in Ada:
http://stackoverflow.com/questions/4988438/ada-string-concatenation

The link below shows the differences between Java and Ada:
http://www.radford.edu/~nokie/classes/320/strings.html