I'm not familiar with Frontpage as I've never used it, but I'm thinking that in order to fix this, you'll need to go outside of Frontpage.
First, close completely out of Frontpage by saving and then hitting the "X" at the top right. If you do not, your changes may simply get overwritten, which wouldn't be good.
Second, browse to your website's files in Explorer and go to the file "_themes\strtedge\strtedge1011.css" and open it in Notepad. Once in Notepad, open up the Find dialog by hitting Ctrl+F and search for the word "transparent". The very first result will get you a bit of code looking like so:
Code:
TABLE{
table-border-color-light:#CCCC99;
table-border-color-dark:#999966;
border-color:#999966;
color:transparent;
}
You need to remove the line with "color:transparent" so that it looks like the following instead:
Code:
TABLE{
table-border-color-light:#CCCC99;
table-border-color-dark:#999966;
border-color:#999966;
}
Once you make that one change, save the file and exit Notepad. You should then be able to re-open Frontpage and publish your website and it SHOULD work again.
EDIT: Also, you may want to consider not using Frontpage in the future -- Microsoft discontinued support for it ages ago and it no longer receives any form of updates. Microsoft Expression Web and Adobe Dreamweaver are two replacement products you may wish to look into