2
I had the same problem just a few hours ago.
I found this and it worked.
MAKE SURE YOU BACK UP YOUR ENTIRE DATABASE BEFORE RUNNING THE SQL INSIDE PHPMYADMIN
INSERT INTO `[xoops_table_prefix]_tplfile` VALUES (1466, 1, 'system', 'default', 'system_block_dummy.html', 'Dummy template for custom blocks or blocks without templates', 1129639910, 0, 'module');
INSERT INTO `[xoops_table_prefix]_tplsource` VALUES (1466, '<{$block.content}>');
GOODLUCK
Arowana