Variable Virtual Table column reference

Hi guys,

I need to combine select column from two tables and then run a calc over the top of the union of these two tables but am having trouble pulling out the reference columns and running the calc. For some reason, it doesn't want to recognise the column names from the variables above. 

below is the code I'm using 

Combined Weighted Avg LVR = 

var c_pipelinetable = SELECTCOLUMNS(FILTER('DB Pipeline','DB Pipeline'[Pr] = "xxx"),
                                     "c_Account", 'DB Pipeline'[Application ID],
                                     "c_LVR_by_Loan_Amount", 'DB Pipeline'[LVR by Loan Amount],
                                     "c_Loan_Amount", 'DB Pipeline'[Loan Amount])

var c_settledtable = SELECTCOLUMNS(FILTER('Dataset - Development Environment',CONTAINSSTRING('Dataset - Development Environment'[Product_Description],"xxx")),
                                    "c_Account", 'Dataset SPV - Development Environment'[Account_Number],
                                    "c_LVR_by_Loan_Amount", 'Dataset SPV - Development Environment'[LVR by Loan Amount],
                                    "c_Loan_Amount", 'Dataset SPV - Development Environment'[Principal_Balanace])

var _PipelineSettled_table = UNION(c_pipelinetable,c_settledtable)

return

CALCULATE(sum(c_Loan_Amount))