Question: internal error in Typesetting:-Parse : "invalid subscript selector"

I encountered a weird error while computing a set of integrals.

Here is my complete code in a .mw file
 

Download Inflow_distribution_for_forward_flight_(teetering_rotor).mwInflow_distribution_for_forward_flight_(teetering_rotor).mw

 

At the bottom I have an error message :"Error, Got internal error in Typesetting:-Parse : "invalid subscript selector". 

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