The below is the error which I received.
Tag Times in Times[Blank[Times[-500.0, Plus[Times[0.2, Cos[theta[t]], Power[Derivative[1][phi][t],
2]], Times[-2, Sin[theta[t]], Derivative[1][theta][t]], Times[0.2, Sin[phi[t]], Derivative[2][phi][t]], Times[2, Cos[theta[t]], Derivative[2][theta][t]]]]], Pattern[two, Blank[part]]] is Protected.
Tag Times in Times[Blank[two], Pattern[two, Blank[part]]] is Protected.
Recursion depth of 1024 exceeded.
Uncaught Throw[TerminatedEvaluation[RecursionLimit], TerminatedEvaluation[RecursionLimit, 1024]] returned to top level.
Tag Times in Times[Blank[Times[-500.0, Plus[Times[0.2, Cos[theta[t]], Power[Derivative[1][phi][t],
2]], Times[-2, Sin[theta[t]], Derivative[1][theta][t]], Times[0.2, Sin[phi[t]], Derivative[2][phi][t]], Times[2, Cos[theta[t]], Derivative[2][theta][t]]]]], Pattern[two, Blank[part]]] is Protected.
Tag Times in Times[Blank[two], Pattern[two, Blank[part]]] is Protected.
Recursion depth of 1024 exceeded.
Uncaught Throw[TerminatedEvaluation[RecursionLimit], TerminatedEvaluation[RecursionLimit, 1024]] returned to top level.