How can i solve this

If the file is on a network server, then try and please first download oit to computer and then open it. If that does not work:

Your file is probably corrupt.

Do you have a backup? 

If you do not have a backup, then the best time to come up with a backup strategy is now. YOu have to regularly save your files. So that when this happens, you do not need to begin from scratch.

Please do also take a look at this: https://helpx.adobe.com/illustrator/kb/illustrator-support-networks-removable-media.html 

Is the filesize reasonable? Like: not 0KB?

In that case, the Illustrator team might take a look at the issue.