I was able to get the query to run by removing the & symbol.
SELECT IIf(DCount("*","dbo_CMC_PRPR_PROV","TaxID = TaxID")>1,"Multiple",[PRPR_NPI]) AS PRPR_NPICalc, ProviderList.TaxID
FROM ProviderList INNER JOIN dbo_CMC_PRPR_PROV ON (ProviderList.TaxID = dbo_CMC_PRPR_PROV.MCTN_ID) AND...