Well, given the information you've provided, I'd s'pose that you have the cable ends terminated wrong/poorly.
The pair-order of the cable at the connectors is critical for high-speed.
Looking at the connector from the rear, clip down, the pair-order should be (left-to-right):
White-Orange, Orange, White-Green, Blue, White-Blue, Green, White-Brown, Brown.
(the above is a "568 B" configuration, you also have the option of exchanging the Green and Orange pair to be a "568 A" configuration).
If you ordered the wire such that each color-pair is grouped (wo,o,wg,g,wb,b,wbr,br), then the specific problem is a split pair on 3 & 6 (your using one wire of one color-pair for signal, and one wire from another color-pair for signal ground..it throws the noise rejection right the F--- out the window...)).
There are also a bunch of rules for how much of the wire can be expeosed out of the jacket (0.5 inch), bend radius, pulling tension (How hard did you pull the cable when installing it? Did youstretch the cable?)....Check out the tech library at Anixter.com and read some of the 568 spec on termination.
Good Luck
Scott