Actually, this is an error that is mostly associated with GP 2013, as Mr. Mariano Gomez mentioned that "Smart list performance needed to improve to make the export functionality usable over Web Client"
The good news that there is a solution; not supported yet, provided by Ms. Leslie Vail, it included adding up a new line ( SmartListEnhancedExcelExport=TRUE ) to the Dex.ini Although, You need to be careful, as the solution is not supported and might have ramifications as stated by Mr. Leslie.
You can review the discussion on the link below;
Adjust Smart List Decimal Places
Best Regards,
Mahmoud AlSaadi