"Bad Request: the message can't be forwarded" doesn't say why

[php4fan]

A bot of mine got this response to a forwardMessage request:

Bad Request: the message can't be forwarded

This message should include the reason WHY the message couldn't be forwarded.

[levlam]

There can be a lot of simultaneous reasons WHY a message can't be forwarded. You can find possible causes of the error in the description of the method at https://core.telegram.org/bots/api#forwardmessage. In any case, the specific error message must not affect handling of the error, for which must be done solely using the error code.