Using ArcGIS 10 SP4 and used the add table to layout option. This is all within ArcGIS, this is not an external table. When exporting to PDF within ArcMap, the grid lines in the table do not print. I've searched archived forum and found a post, but this issue was not resolved. I can export to PDF or print natively without issue. I do not have full acrobat but do understand that if I used the Acrobat printer, it would render the PDF correctly. Looking for the check box that makes this work.
There is no magic checkbox; you have instead run into a long standing problem for many users, sometimes on a hit or miss basis. There are numerous workarounds such as using the print to pdf as suggested. There are several good and free pdf printers. Another option that preserves the layers and georeferencing information involves copying and pasting the table from Excel but even that isn't perfect. So we often use the table to create a stamp and add it in Acrobat to the pdf but you unfortunately don't have that option.