Yes, you are scheduling too many programs and your TiVo is worried that it may have to delete some stuff earlier than planned to make space for what you've asked it to record.
There are two basic reasons people get this message: They just need a bigger TiVo, or they've set a whole bunch of stuff as KUID.
The reason KUID is relevant is that when your TiVo calculates space, it assumes you will NEVER delete KUID recordings. So if you have a lot of shows set to record KUID, it looks at your ToDo list and sees that it may run out of space since those recordings will be around forever. If you DO actually delete some things and free up some room, it may not actually delete anything earlier than planned, but it is warning you of the possibility.
If you have saved stuff on there, make more space my deleting it or moving it somewhere else or changing it to delete as space needed. If you have a lot of stuff set to record as KUID, change them to until space needed. It will make your TiVo a lot more usable. If you just are scheduling a ton of recordings, then yes, consider making your TiVo bigger or adding a second one. You can upgrade yourself if you're computer-savvy, ot you can just buy a big drive from someplace like weaknees.
Also keep in mind that save "until space needed" does NOT mean it will be deleted right away, or even anytime soon. I have recordings on my TiVo that are more than a year old and have just been hanging out. It just depends on how much other stuff is scheduled. But if you record everything as KUID, you really cripple your TiVo b/c its space calculations assume those recordings will stick around forever.