Background: I created a table a couple of weeks ago, for a new, under-construction website. It is a wide table with lots of fields. Based on another public support answer, I added some custom css to control the widths of some fields, and to preserve wordwrap:

table.wpDataTable td {    white-space: normal !important;
}
.wpDataTableID-1 th.column-id {   
   width:80px !important;
}
.wpDataTableID-1 th.column-title {   
   width:345px !important;
}
.wpDataTableID-1 th.column-studyconductedby {   
   width:365px !important;
}.

.wpDataTableID-1 th.column-mainfindings {   

   width:420px !important;
}

In the Study Conducted By field (string / multi line edit - same settings as the Main Findings field, which seems to have no problem), I tried to add text. The text, including newlines, is near 256 characters (which maybe is significant?). If the text is short enough, no problem. If I add a few more characters, of any sort, I am unable to updat the record and get a message: 

"There was an error trying to update the row. Error: WordPress database error: Processing the value for the following field failed: studyconductedby. The supplied value may be too long or contains invalid data."

I have similar fields (e.g., Main Findings), which have longer values- no problem. I plan to have thousands of records in this table. I hope there's an easy solution - or that it's a user error. Thank you.

Thank you; will do. BTW, I had written a reply; at some point along the way, it didn't get saved or sent or something. Anyway, here's the gist:

I have a hunch. This happened when I created a new field, "Conducted By (2)". I noticed that you can specify one-line string or multi-line string as the data type when creating the column. But I could find no distinction in settings - once the column is created - for one-line vs multi-line string. I created the original field, "Conducted By" - the one with the problem - as a single-line string. I created the replacement field, "Conducted By (2)", as a multi-line string. With the replacement field, I can enter the data that was giving me problems on Conducted By, and it's fine. No problems.

Could it be that the issue is caused by originally defining Conducted By as a one-line string? And, if so - and in any case - is there a way to change that once the field is created? (Changing edit to multi-line apparently makes no difference in this case.)

I realize my hunch could be totally off.

Thanks,

Gary

FYI, I just had this happen with another field. It was defined (I'm pretty sure, retrospectively), as a single-line string, and right around the 256-character mark, it will not let me add any more text. If there was a way to change this, basically converting the field to a multi-line string, - if this is the issue - that would be great.