Hello Anindya,
I have consulted with a Principal Research Statistician in the risk organization. He says that when risk complains about an aggregation having missing sensitivities, it is not complaining about the covariance or correlation matrix. Aggregations are subportfolios. The error is telling you that some subportfolio has missing values for its sensitivities. Either the value of a position is missing at perturbed Delta Normal state or the pricing method sets rf.der to missing for some risk factor. An error might seem extreme for this kind of problem, but any missing value invalidates the calculation of VaR for that subportfolio. As lower-level sensitivities percolate to the portfolio level, the portfolio level thus contains the same missing values, which invalidates the calculation of VaR there. We recommend you check your positions for missing values.
I hope this helps,
Michael Harvey
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