triplegolf - not only the source code length counts!
Bash, 23 characters
Error:
bash: /: Is a directory

Source:
echo       $0-$01234;/;

Output:
/bin/bash-/bin/bash1234


Brainf*ck, 32 characters
This code executes for about 3 seconds and stops and displays the following error and output.
Error:
bff: out of memory (-2058691272)

Source:
+++++[......-]..+[&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;-]

Output: (Hexdump)
0505 0505 0505 0404 0404 0404 0303 0303
0303 0202 0202 0202 0101 0101 0101 0000


C, 35 characters
Warning:
b.c:1:30: warning: division by zero

Source and Output:
main(){system(&quot;cat &quot;__FILE__)/0;;;}


PHP, 50 characters
Warning:
PHP Warning:  Division by zero in /tmp/3 on line 1

Source and Output:
&lt;?php echo (0/0).''.file_get_contents(__FILE__);?&gt;