Have you just changed the ink cartridges?
Are the ink cartridges Epson or compatibles?
Is the magenta ink running out?
Do you have a program running like 'Inksaver'?
1. Make sure the tape which you have to remove from the cartridge has come off properly. If there is some left, it can starve the printer of ink but only after a while depending on how much air is getting in.
2. Get a new cartridge and see if the problem disappears.
Have you left it for a long time without printing?