Both of the connection strings are wrong.
For .xlsx, it should be:
StrConn = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" + srcFile + ";Extended Properties=\"Excel 12.0 Xml;HDR=YES;IMEX=1\";";
(Note the extra Xml part, the HDR=YES to indicate your file has headers, the IMEX=1 to treat all data as text and the repositioned semi-colon. You would need different connection strings for .xlsm and .xlsb files - see here)
For .xls, it should be:
StrConn = @"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" + srcFile + ";Extended Properties=\"Excel 8.0;HDR=Yes;IMEX=1\";";
(Note the change from Excel 1.0 to Excel 8.0 and the addition of a semi-colon at the end)