50xxx · The file itself
CESOP error 50010
“The XML message is not well formed”
Caught before you file
What it means
The file is not well-formed XML, so CESOP cannot read it at all and nothing in it is processed.
Why files get it
- Unescaped characters — an ampersand in a name is the usual one.
- A file cut off during export or transfer.
- An encoding mismatch between the declaration and the content.
How to fix it
- Fix the XML at the line the parser names, then check the file again: until it parses, no other rule has been applied.
Check a file for 50010 before you submit
The free validator runs the CESOP business rules against your file and names the error each finding would become — 50010 included — so the Validation Result is not where you first hear about it.
The file is parsed in your browser tab. No upload, no account.
Source: the error catalogue in the Payment Data XSD User Guide — CESOP, v4.40 (DG TAXUD), §2.2.3.18. The explanation is ours; it describes the file format and is not tax advice.