Have you verified the things that the last message talks about?
Is the URL in site.conf https://mpt25.math.sc.edu? And is that the base URL of the link you created in Blackboard?
Is the consumer secret in conf/authen_LTI_1_1.conf in the variable $LTI{v1p1}{BasicConsumerSecret} exactly the same as the consumer secret set for the external tool in Blackboard?
Is the URL in site.conf https://mpt25.math.sc.edu? And is that the base URL of the link you created in Blackboard?
Is the consumer secret in conf/authen_LTI_1_1.conf in the variable $LTI{v1p1}{BasicConsumerSecret} exactly the same as the consumer secret set for the external tool in Blackboard?