Apparently it's rude to say "no problem"?

My manager asked me to do something, and I replied with "sure, no problem." She really didn't like that and said to never talk to her like that again. I am entirely confused, as that has always been a genuine phrase for me to say.

Some research on Google suggests that older folks, born before 1980-ish, tend to find this phrase distasteful. My manager is 50ish, but what in the world? I have never once heard that "no problem" could be interpreted as rude.