Error 90122 means a field in your file carries HTML or other markup. Amazon's fields take plain text. A cell that contains formatting tags, such as the tags a web page uses for bold text, links, or line breaks, returns error 90122.
The processing report gives five entries for each failed row: the record number, the SKU, the error code, the type, and a message. Record 1 is row 3 of your file, so the row for a record sits at the record number plus two. For error 90122, the message names the field that carries the markup. The report does not show the markup itself. The tags sit inside the cell in your file, and the file is where you read them.
A flat file is a table of plain text values. The description fields are where markup arrives most often, because descriptions are usually written somewhere else first and pasted in. The pasted text brings its formatting with it, as tags inside the cell. Amazon reads the whole cell as the field's value, tags included, and returns the row until the cell carries plain text only.
A submission can carry errors that sit outside the file. A missing brand registration or approval returns error 5665. A missing permission to list in the category returns error 8026. Editing the file does not repair either one. The diagnosis lists those errors separately, with the reason and the step to take in Seller Central, and we do not call them fixed.
The free diagnosis reads your failed file and the processing report Amazon returned. It shows every error by SKU, states which errors we fix automatically, which ones need your answer, and which ones the file cannot fix. Removing markup is one of the fixes we apply automatically. You can start from the FixFlatFile home page.
Requirements differ by category, and Amazon decides whether a file is accepted.