If the same buffer for preparing the lysate is used as the control, you should be able to make a standard curve with the same buffer, and make sure your ELISA works. If you have reducing agents or detergent like SDS in your lysis buffer, then this is the likely cause as Stephane has suggested. But you can test your buffer effect by adding it to your standard that comes with the ELISA. So no matter what buffer you use, you need to add an equivalent amount of it to your standards as you would use with your sample.