Cannot insert a row in what appears to be a table in a worksheet

When I attempt to add a row I get the following mesage:

This operation is not allowed. The operation is attempting to shift cells ina table on your worksheet.

I did not create this, but I cannot figure out how it is locked in this manner without any file or sheet protection that I can see. Thanks in advance to anyone who can offer a solution. I tried to attach the file, but was informed that it is too large.