darkening of background when reading library books

using adobe ade/library books fine, after 6 or 7 times of returning to said book, the screen slowly darkens. Only solution so far is to un-install/re-install adobe, then after 5 or 6 times I have the error ..to many activations, can someone help.  I am using Aldiko reader and Samsung Galaxy Android 10.1 tablet, any ideas please as I am now getting desperate. Thanks