In Brian Carroccio's article (part 2) that looks back at past Indy Car CEOs, it says:

In July of 2000, Rahal along with Texas Motor Speedway President Eddie Gossage announced there would be a 2001 CART race at the 1.5 mile oval.
Of course, that race would ultimately be cancelled as drivers found the speeds too dangerous.
The race was cancelled because CART discovered, just prior to the race, there were physical laws of nature that made it impractical to race CART Indy cars there at speed.
The slower IRL cars could race there, and had, with no problems related to physical laws of nature.

The story of how the race came to be cancelled is covered in chapter 33 - CART Screws Up Big Time - of Dr. Stephen Olvey's book - Rapid Response.

The medical staff determined the issues that led to the cancellation of the race.
However, Olvey says some drivers did express reservations to him about the track before they actually went there.

Testing at the track was done by Rahal's team on a "very cold" winter day, which limited the test car's top speed to 206 mph. Kenny Brack was the test driver.
Wally Dallenbach and Kirk Russel went on record against having an event at that track after just driving around the track in a rental car. They didn't like the sharp increase in angle going from the straights up onto the banking. Dallenbach and Russel also suspected that the cars would be going so fast at that track that safety would be compromised.
Some speculate that Rahal had his own agenda, but those voices in and out of CART that expressed concerns about the track were overruled/ignored.

After incidents both on and off the track during practice, CART's medical staff discovered that the banking angle and car speed (232 mph average practice speed) was causing drivers to suffer vertigo and/or G-LOC (G-force induced Loss Of Consciousness).

Olvey was given permission to look at proprietary G sensor information from Paul Tracy's car.
That information showed that drivers were being subjected to concurrent vertical (about 3.5G) and lateral G's (about 5.5G), something not previously experienced to that degree by open wheel race car drivers. Jet fighter pilots of the day didn't experience concurrent vertical and lateral G-loads either, and wore a G-suit when they expected to encounter more than 4G. In other words, there was no scientific literature about what happens to people subjected to concurrent vertical and lateral G-loads.

An emergency driver's meeting was called and it emerged that 18 of the 20 drivers had experienced symptoms related to excessive G-loading. The 2 drivers that had no symptoms had done less than 4 consecutive laps.
All 20 drivers would have likely had debilitating G-LOC symptoms after 6 or more laps during the race.

A meeting of CART management, team owners, track management, and tire/engine reps lasted 9.5 hours exploring ways to slow the cars down enough to avoid the driver G-loading problems.
No solutions were found, so the race was cancelled.

http://en.wikipedia.org/wiki/G-LOC