Hi Monique
Did you check if the version of excel used in the Mac is same as that in the PC ?
Also please see if it is specific to a business object say SC or for all ..
Lastly please have a look at the below OSS notes if this does not help I suggest you open a note to SAP for further investigation .
The note states " When you Save the excel file in your local file system. Now try to open the saved excel file from the local file system. While openeing the excel file it throws an error message 'Excel found unreadable content "
This is due to a program error. This is a generic issue with the new excel framework and not specific to any Business Object.
This issue will appear only if the the customer is using the new excel UI and only if the switch SRM_702_EXCEL_UP_DOWNLOAD is active. This fix is not needed for releases lower than SRM 7.0 EHP2.
Also check the below notes :
1612239 - SRM7.0(EHP2): Upload/Download of documents using MS Excel
1727066 - Excel Download: Template Sheet Repair
734060 - SRM: Upload and download of documents using MS Excel
734060 - SRM: Upload and download of documents using MS Excel
734946 - SRM: Restrictions for upload and download
982766 - Cons Sol:Up and download of SRM documents to MS Excel (PDUD)
Regards
Vinita