It's amazing. I did a serach on the same problem with my Sony DCR-TRV250 and found your message. I've had this camcorder for about 3 years and mine just startd doing the exact same thing as yours. It only seemed to start after I charged the battery. I got it to go away twice somehow by removing the tape several times and replacing it with another tape (used) along with removing the battery and replacing it. I did this repeatedly in some combination and it worked but now I can't get it to go away. I still get the blinking triangle. Maybe I'll try a brand new tape. It hasn't been exposed to any abnormal moisture as this triangle might indicate but it says to remove the tape and leave it open in a dry place for one hour if you suspect moisture.
I was hoping to find someone to talk to at Sony or some repair shop. I wish I had some answers but hopefully someone else does. PLEASE keep me informed.