According to CVG, a source revealed that the downloadable series update "fails the epilepsy tests so much that it has to be re-engineered."
The game was previously slated to debut this summer, but was delayed due to unspecified technical issues. Sony Entertainment Europe CEO David Reeves described them as "tricky technical problem" which none of Sony's studios have yet been able to resolve.
People afflicted by photosensitive epilepsy can experience seizures triggered by rapid visual stimuli such as flashing lights or moving patterns. Many games including elements which could possibly prompt such seizures often include epilepsy warnings either in-game or in a title's instruction manual.
Sony has not yet made an official statement detailing why the game was delayed, though Reeves noted that he expects Wipeout HD to arrive before the end of the year.