Dimension mismatch error in simulink

I am attempting to feed simulated GPS and inertial sensor data to the simulink EKF block. The entire model runs fine when the EKF block is NOT connected. However when connected, a dimension mismatch occurs to a summing block that is a few sub-systems upstream of the EKF block. There is no direct connection between the EKF block and the upstream summing block where the error is being generated : _Error in port widths or dimensions. Output port 1 of 'Quad_Matlab_EKF_attempt/INS Subsystem/Sum7' is a [1x1] matrix.

Is there a known simulink issue regarding a possible backpropagation to upstream blocks? If so, any known fixes?