This is one of those sceptical claims that makes you scratch your head and say "Hunh"? Sometimes, the search for contradictions in the Bible can take a decidedly desperate turn. Let's look at the two passages below:
"The LORD standeth up to plead, and standeth to judge the people." (Isaiah 3:13)
"Let the heathen be wakened, and come up to the valley of Jehoshaphat: for there will I sit to judge all the heathen roundabout." (Joel 3:12)
I must ask: Where is the contradiction? God stands in one passage, God sits in the other passage which is dealing with an entirely different set of circumstances. God is presented anthropomorphologically in both verses, but is in different circumstances contextually. Any one of us stands in some circumstances, and sits in others. The one does not preclude the other, and hence, a contradiction between these two verses cannot logically be claimed. Just goes to show that there are some folks out there who haven't yet mastered the Law of Non-Contradiction. This one should probably be chalked up to nothing more than desperation on the part of sceptics.