I am facing input string issue suddenly. previously my code is running 2018 version and in windows 7 environment. now we migrated the code to Win10 and UiPath 20.10 version. once we moved the code facing this issue.
The issue may mostly arise when converting to Int64 Type, instead you can try
(From x In io_dtLookupReport17
Join y In in_dtReport17 On Integer.TryParse(x("Loan Ac No.").ToString.Trim,0) Equals Integer.TryParse(y("Loan Ac No.").ToString.Trim,0)
Select io_dtLookupReport17.Clone.LoadDataRow(New Object(){x("Loan Ac No.").ToString,y("Current MIA").ToString,y("UDF Tagging Account"),y("UDF Tagging Customer")},False)).CopyToDataTable