Customers are lined up to buy Microsoft’s new Surface Book model, the one with a roomy one-terabyte (TB) flash drive. But there’s a problem. They can’t get their hands on it—or even place an order.

In fact, right now, the best consumers can do is request notification for when Microsoft’s self-proclaimed “ultimate laptop” will be available again.

Update: Microsoft updated its site later on February 16. It is now taking Surface Book orders again with units to ship March 4.

Microsoft started taking pre-orders for the convertible laptop in October. The 1TB model was due to ship by Jan. 22, 2016.

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A Microsoft spokesperson said those units did, indeed, ship. Well, most of them, at least. But now there is no more stock available, due to higher-than-anticipated demand, she said. Microsoft is working to respond to demand as quickly as possible, she noted.

The spokesperson was unsure if a lack of flash drives or larger screens (which are impressive, by the way) caused the shortage. Or perhaps Microsoft trying to inflate pent-up demand for its high-end, $3,199 model. Your guess is as good as mine.

A would-be buyer who alerted Fortune to this issue already owns a Surface Pro with 8GB of RAM; a 512 GB solid-state drive (SSD); and 12-inch screen. His verdict? Not bad at all, except for the fact he needs more memory, a bigger drive, and a bigger screen. And he’s willing to pay for it, if only he could.

In his view, the Surface Book model with 13-inch screen, 16GB of RAM and 1TB SSD would be the perfect laptop.

“I really think Microsoft got it right this time,” he said via email. “But I’m still waiting to find out.”

Microsoft Wants to Push Surface Pro into Big Business

With Microsoft’s new Surface Pro and Surface Book franchises, it looks like the company finally has a solid response to Apple’s aapl popular iPad Pro and MacBook Pro tandem—streamlined, light-weight units with crisp screens. Oh, and none of the crapware that is typically installed on Windows laptops made by third-party hardware makers.

But if Microsoft really wants to steal mind- and market-share from industry leader Apple, it’s got to deliver what it promised.

This story was updated at 5:00 p.m. February 17 to reflect that Microsoft is again taking orders for the Surface Book.