SQL error on moving topics

Hope I am in the right place -
when I move topics I get this (but it still works - possibly it has something to do with the fact that our database became corrupt when we did the Conversion - does this provide a clue to what happened - the topics are there but no posts which is why I am moving them):
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General Error
SQL ERROR [ mysql4 ]

Out of range value adjusted for column 'forum_posts' at row 1 [1264]

SQL

UPDATE phpbb_forums SET forum_posts = forum_posts - 11, forum_topics_real = forum_topics_real - 1, forum_topics = forum_topics - 1 WHERE forum_id = 5

BACKTRACE

FILE: includes/db/mysql.php
LINE: 158
CALL: dbal_mysql->sql_error()

FILE: includes/mcp/mcp_main.php
LINE: 715
CALL: dbal_mysql->sql_query()

FILE: includes/mcp/mcp_main.php
LINE: 93
CALL: mcp_move_topic()

FILE: includes/functions_module.php
LINE: 471
CALL: mcp_main->main()

FILE: includes/functions_module.php
LINE: 766
CALL: p_master->load_active()

FILE: mcp.php
LINE: 168
CALL: p_master->load()