The Row Operations Package needs to be loaded.
Maple is willing to work with function calls it has no recipe for explicitly calculating.
Maple Release 4 uses backquotes, not apostrophes, for strings. The error message below comes from Maple having noticed a clon in a syntactically wrong position. You may see a display like this in which it appears that the computer has made an arithmetic error. Here first swapping rows 1 and 2 makes the matrix appropriately triangular. For matrices with floating point entries, small roundoff errors prevent ordinary back substitution from being used.