shortlinks suddenly calling a header error

All of the shortlinks on my blog are suddenly causing an error:

***
Warning: Cannot modify header information – headers already sent by (output started at /nfs/c03/h01/mnt/51914/domains/knithacker.com/html/index.php(1) : eval()’d code:37) in /nfs/c03/h01/mnt/51914/domains/knithacker.com/html/wp-includes/pluggable.php on line 897
***

Here’s a sample shortlink: http://wp.me/pjlln-1lc
which goes to: http://knithacker.com/?p=5158
but should actually go to: http://knithacker.com/2011/06/26/we-can-do-it-rosie-the-riveter-amigurumi/

Any ideas?