Thanks very much for the tip. It seemed to be exactly what was needed. It said that it was because there was a limit of about 3450 characters in the field and that this was exceeded. To solve it said:
If you must enter a large amount of text in the Memo field, delete the index for the Memo field. To do so follow these steps:
Open the table with the Memo field in Design view.
On the View Menu, click Indexes.
Click the index for the Memo field, and then delete it.
Unfortunately, you must then, of course, save the table, but when doing so, it informs that the index field must have a name. So why Microsoft shows this as a solution seems ridiculous.