That error message appears (specifically) when it does not detect any data that it can convert. That is a specific error message that only appears when it doesn’t detect any data that it recognizes. It is not like the FM CONVERTER is not working — it is very much working. If it did nothing (showed no error message) that would indicate it is not working.
What is the source of this data (which FM instrument)?
I try any kind of data my own and from different web sites and the result is the same. Try also different browsers... same!
Bad Mister, can you send me a .syx file which work to you to try convert.