GriffinDWolf,
It is always best to wrap up a Teamwork project by going to File > Save as... Format= PLN (ARCHICAD Solo Project) or PLA (ARCHICAD Archive Project) and then delete the project from the BIM Server to clear out the dead weight. The PLN or PLA can then be opened by any future version of ARCHICAD.
.BIMproject files are version specific. You must re-import the file into the version of BIM Server it was created from. Based on the date and file extension, I would guess the file was probably exported from BIM Server 14 or 15. Once the file is re-imported to the corresponding version BIM Server then you may Join the project via ARCHICAD 14 or 15, save as a PLN and then open the file in ARCHICAD 18 and share to BIM Server 18.
I have uploaded the installers for BIM Server USA 14 and 15 in case you do not currently have a running BIM Server 14 or 15 module (links expire 2015-09-11):
BIM Server 14 USA for Mac OS X (64 MB)
BIM Server 14 USA for Windows (64-bit) (71 MB)
BIM Server 15 USA for Mac OS X (55 MB)
BIM Server 15 USA for Windows (64-bit) (71 MB)
For the most ease I recommend installing BIM Server 14/15 onto a different computer than your current operating BIM Server computer. You could install it on your ARCHICAD workstation. That way when the software has served its usefulness and the File has been saved out as a PLN you can then go to the BIM Server folder and double-click the Uninstall BIM Server alias to remove the BIM Server software.
I hope this helps.
Best regards,