Don't understand the relationship between a combo box and a table

Hi there

Currently I am getting the following message:

"The operation failed. There are too many indexes on table 'Orders'. Delete
some of the indexes on the table and try the operation again."

In my table, I am trying to change a text box into a multi=select combo box.

There are 45 fields in my table of which 40 have this multi-select combo box.

I don't understand where these indexes are being created.

I do have 1 primary key in my table.

Thank you