The decision to further delay the launch was made Sunday after Boeing engineers discovered that a band of insulating cork on the first stage wasn't sticking to the rocket as it was supposed to.

The problem first was discovered last week and caused a launch slip of three days while repairs were made. But following a launch attempt Saturday night Boeing engineers discovered the cork was not sticking in places and decided they needed to effect repairs.

"They don't fully understand what the problem is,'' said NASA spokesman George Diller. "If it's not adhering to the vehicle, you don't get the full effect of the insulation. It has to adhere to be sure it's doing its job.''

Bands of cork surround the first stage of the rocket near the places where the nine strap-on solid rocket boosters attach to the Delta 2 Heavy, a new version of the workhorse rocket that features larger and more powerful strap-on motors.

The earlier work involved replacing an entire band of cork and patching areas of a second band -- repairs that apparently didn't take hold. It's not clear what would happen to the rocket if the cork broke free during launch.

Although the material and technology is different, the launch industry is particularly sensitive right now to falling debris at launch as this was the likely event that set up conditions which led to the loss of shuttle Columbia and its seven crewmembers on Feb. 1.

Having confirmed there still are problems with the Delta 2's cork band, officials have ordered a new round of repairs that will keep the mission grounded until Wednesday.

A Wednesday liftoff from Cape Canaveral Air Force Station's pad 17B would be at either 11:17:37 or 11:59:54 p.m. EDT (0317.37 or 0359.54 GMT).

Saturday night's launch attempt was scrubbed due to a variety of reasons involving weather and range safety rules.

The first attempt just before midnight was officially delayed because of a boat in the launch danger area and winds that were blowing in a direction that would endanger the public should the rocket explode shortly after liftoff.

The second available opportunity early Sunday morning was called off because of unacceptable upper level winds.

Technically everything went well with the countdown and both the Delta 2 Heavy and the Mars Rover Opportunity spacecraft behaved themselves during the procedure.

Opportunity has until July 15 to get off the ground or it will miss its planetary launch window and chance to join its twin probe Spirit, which was launched from the Cape on June 10.