Excel 2010 - problem adding spreadsheets to a Word document.

When I try to import an '.XLSX' file into a Word 2010 document and then convert it to BPF I get the following error "There isn't enough memory to complete this action.  Try using less data or closing other applications.  To increase memory available, consider:  Using a 64 bit version of Microsoft Excel - Adding memory to your device."

The next error (most of the time but not every time) is "We found a problem with some content in file.xlsx.  Do you want us to try to recover as much as we can?  If you trust the source of this workbook, click yes'

My PC has 10 Gb of RAM with a 16,000 Mb page file on the C drive!
The Excel spreadsheets I am working with are very small.  All less than 1 Mb.

If I reboot, I can often get it to work.  But don't understand the reason for the problem.

Thanks