The most likely cause of this problem is where the admin of the forum has tried editing the style templates, but they have made a mistake making all the pages blank.

To fix the problem the following tables need changing (in phpMyAdmin or database manager) this will revert the phpBB styles back to default:

• Table: accessname_config – Change row: override_user_style to: 1
• Table: accessname_config – Change row: default_style to: 1
• Table: accessname_themes – Truncate/Empty the table and then run the following query:
  
  INSERT INTO `accessname_themes` VALUES (1, 'subSilver', 'subSilver', 'subSilver.css', '', 'E5E5E5', '000000', '006699', '5493B4', '', 'DD6900', 'EFEFEF', 'DEE3E7', 'D1D7DC', '', '', '', '98AAB1', '006699', 'FFFFFF', 'cellpic1.gif', 'cellpic3.gif', 'cellpic2.jpg', 'FAFAFA', 'FFFFFF', '', 'row1', 'row2', '', 'Verdana, Arial, Helvetica, sans-serif', 'Trebuchet MS', 'Courier, \'Courier New\', sans-serif', 10, 11, 12, '444444', '006600', 'FFA34F', '', '', '', NULL, NULL);
  
  
• Table: accessname_themes_name – Truncate/Empty the table and then run the following query:
  
  INSERT INTO `accessname_themes_name` VALUES (1, 'The lightest row colour', 'The medium row color', 'The darkest row colour', '', '', '', 'Border round the whole page', 'Outer table border', 'Inner table border', 'Silver gradient picture', 'Blue gradient picture', 'Fade-out gradient on index', 'Background for quote boxes', 'All white areas', '', 'Background for topic posts', '2nd background for topic posts', '', 'Main fonts', 'Additional topic title font', 'Form fonts', 'Smallest font size', 'Medium font size', 'Normal font size (post body etc)', 'Quote & copyright text', 'Code text colour', 'Main table header text colour', '', '', '');

Just replace accessname with the forums real access name on all the table names and query commands above (which are highlighted in bold). If this doesn't cure the problem delete the forum from the Multi-Forums admin page and tell the user to setup the forum again.