channel_data column limit reached

Hi folks

I have an EE project which is running 10 sites using MSM.

I have hit the limit for number of columns allowed in the channel_data table, meaning I can no longer create custom fields.

The table engine is MyISAM. I’ve read that InnoDb has greater limits so thought I might be able to convert the table Engine to that. However I cannot convert the current table, or set up a new table with the same structure as I get an error ‘erno:139’

I’m really stuck on this now and cannot complete the project.

Has anybody found a solution to this?

Cheers Darren