XLSX Multi-file switching error

I just ran a graph which tries to load data from 5 xlsx files each which shares the same columns (metadata). The run failed with the below:

ERROR [WatchDog] - Node XLS_READER0 finished with status: ERROR caused by: Component pre-execute initialization failed. An error occured while switching input file C:\Endeca\Projects\army_engineers\data-in\FY06 NWD - Labor AE and Construction cost.xlsx, the file will be ignored caused by: jxl.read.biff.BiffException: Unable to recognize OLE stream
ERROR [WatchDog] - Node XLS_READER0 error details:
Element [XLS_READER0:Load Construction]-Component pre-execute initialization failed. An error occured while switching input file C:\Endeca\Projects\army_engineers\data-in\FY06 NWD - Labor AE and Construction cost.xlsx, the file will be ignored caused by: jxl.read.biff.BiffException: Unable to recognize OLE stream
at org.jetel.graph.Node.run(Node.java:418)
at java.lang.Thread.run(Thread.java:662)
Caused by: An error occured while switching input file C:\Endeca\Projects\army_engineers\data-in\FY06 NWD - Labor AE and Construction cost.xlsx, the file will be ignored caused by: jxl.read.biff.BiffException: Unable to recognize OLE stream
at org.jetel.util.MultiFileReader.init(MultiFileReader.java:120)
at org.jetel.component.XLSReader.preExecute(XLSReader.java:594)
at org.jetel.graph.Node.run(Node.java:416)
... 1 more
Caused by: org.jetel.exception.JetelException: An error occured while switching input file C:\Endeca\Projects\army_engineers\data-in\FY06 NWD - Labor AE and Construction cost.xlsx, the file will be ignored caused by: jxl.read.biff.BiffException: Unable to recognize OLE stream
at org.jetel.util.MultiFileReader.nextSource(MultiFileReader.java:275)
at org.jetel.util.MultiFileReader.init(MultiFileReader.java:114)
... 3 more
Caused by: jxl.read.biff.BiffException: Unable to recognize OLE stream
at org.jetel.data.parser.JExcelXLSDataParser.setDataSource(JExcelXLSDataParser.java:405)
at org.jetel.util.MultiFileReader.nextSource(MultiFileReader.java:264)
... 4 more
Caused by: jxl.read.biff.BiffException: Unable to recognize OLE stream
at jxl.read.biff.CompoundFile.<init>(CompoundFile.java:116)
at jxl.read.biff.File.<init>(File.java:127)
at jxl.Workbook.getWorkbook(Workbook.java:268)
at org.jetel.data.parser.JExcelXLSDataParser.setDataSource(JExcelXLSDataParser.java:403)
... 5 more

I am now converting all the files to XLS files to see if that solves the problem. Any ideas?