Difference beetwen awk and gawk?

Hi,
I'm new to awk, I wrote a simple script using gawk, then change it to awk:

awk '/[0-9]+ [a-z0-9]+/{printf " \047%s\047)\n", $1 >
"text.txt"}END{printf "END\n" > "test.txt"}' afile.dat

afile.dat :
123456 abc
111111 abcd

It works with gawk, but in awk returns an error:

..wk: 0602-533 Cannot find or open file afile.dat
  The source line number is 1.
  Syntax Error The source line is 1.


Any ideas? afile.dat has read rights.

Regards, David