Translation upload error

Hello, one translator of mine tired to upload translate file into Crowdin but receives an error - internal server problem. So no info. Anyone faced that in past? How can be solved? This user works offline in another tool (an app for laptop). Hope anyone can advice.

99% sure your mate used some custom xliff that supported only by his/her specific tool.

In that tool should be an option like in MS Word, something like save as or export as - you need to choose just .xliff, a regural (native) one. Once saved in native .xliff format there shouldnt be any issue during translation upload.