Can converting MyISAM to InnoDB cause problems? I am changing an old MySQL database table which is still in MyISAM. I'd like to change it to InnoDB, but I don't know whether it can cause problems and it's a pretty important table so I don't want to break anything.

So my question: can it cause problems when I convert a MyISAM table to InnoDB?
Yes, it can cause a number of troubles.  However, troubles are rare.

All the 'troubles' I know of are listed here.

(Do not change tables in the databases mysql or information_schema or performance_schema; that will cause serious trouble.)