White balance w/EOS utility

[comet]

I just started using an old Rebel XSi to do some photos at work.   I really had no familiarity with this camera or utility but figured out some basics.  I shot an 18% grey backdrop to set a manual white balance and it worked fine.  I retook the backdrop shot a couple times and reset the white balance without issue.

But then for some reason on a reshoot/reset it turned dark.  No matter what I try it still comes out too dark and I can't get anything to look right.  If I set the exposure level higher it sort of gets to where I need to be but every photo then is kind of washed out.   I cannot figure out what changed or why it doesn't work all of a sudden.  I didn't change lighting or the camera in any way.   Any assistance appreciated.

[ebiggs1]

"I didn't change lighting or the camera in any way."

It certainly sounds like something failed.  An XSi is getting along in years now as is its lens.  A sample or two or more would be great help.