Trying to update an old project [ASSERTION FAILURE]

I'm trying to update an old project, and when I try to update the xib files builds for drop down to something more current it crashes. If I'm reading it correctly it looks like a button is giving issues so I tried to delete all the buttons in that xib file, but when I try to save it I get the same crash error as below:

Process: Xcode [2726]

Path: /Applications/Xcode.app/Contents/MacOS/Xcode

Identifier: com.apple.dt.Xcode

Version: 9.2 (13772)

Build Info: IDEFrameworks-13772000000000000~2

App Item ID: 497799835

App External ID: 825038102

Code Type: X86-64 (Native)

Parent Process: ??? [1]

Responsible: Xcode [2726]

User ID: 501

Date/Time: 2018-03-14 14:51:06.147 -0400

OS Version: Mac OS X 10.12.6 (16G1114)

Report Version: 12

Anonymous UUID: 3467F385-51F3-427C-393E-489F819B0011

Time Awake Since Boot: 3300 seconds

System Integrity Protection: enabled

Crashed Thread: 0 Dispatch queue: com.apple.main-thread

Replies

>I tried to delete all the buttons in that xib file, but when I try to save it I get


Did you hit that project with the obligatory 'option-clean build folder' right square between delete and save?