I had this happen a few years ago after getting off at Boylston to take pictures of the PCC and Type 5. I tried to tap back in and it told me to pound sand. I figured it was because of a cool-off period (NYCTA does the same thing), so the wife and I just grabbed ice cream in the park before heading back into the subway.
"That sapling that once grew just south of Wassaic may be long gone, and the Harlem Line’s appearance may have changed over the years, but for decades to come, I can count on it continuing to provide me with funny recollections"