"high speed", huh? :-)
That's a term you tend to see on vendor sites for almost any of them (including some of the cheap "no name" cards that some vendors try to include in package deals to make more profit on the sale).
KM recommends 10mb/second cards for 30 frame per second movies. Popular choices are cards like the larger Panasonic cards, or even the newer Sandisk cards like the Ultra II (although these newer Sandisk cards are not on the "tested cards" list, most users report they work fine).
Note that most cards on the "tested cards" list are not this fast (hence the note at the bottom about movies).
Here is the compatibility chart for your model (outdated now though). Again, see the note at the bottom of the chart about movies.
DiMAGE Z2 Compatibility Chart
I'd try updating your firmware if you haven't done so, too. You could have a problem that the firmware update solved (manufacturers often improve more than what the firmware description leads you to believe).
Firmware Version 1.02 for the DiMAGE Z2
You'll also see a link to the instructions (which will tell you how to check your current version).
If you're not running Windows, see the other optiions:
Konica-Minolta Digital Camera Software and Drivers