Youe Quicktime Pro 7 can only cache 10GB at max, depending on your settings in "Preferences"... That is likely why you're receiving that error. I don't think there's a work around on this since Quicktime does have that 10GB limitation.
You're likely gonna have to find a different app. that is able to handle much larger file size videos.
That's been my observation & experience, anyway. I have to use a professional Video app. to import the video straight from the Cam onto my machine/app for editing etc.
I still have more than 30 GB left. With about 90 minutes tape, I imagine it would represent about 18 GB. Should work. I also tried to use an external HD of 2 TB and showed same error.
Or, if your miniDV has a standard DV FireWire interface, you could try the free Mitz Pettel Vidi DV capture utility. It is somewhat old but seems to still work under Snow Leopard without the capture limitations of QT 7 Pro other than being limited to DV compression mode and FireWire interface.