Excel keeps crashing when opening diagram

So i have a client that is trying to use Excel. When he is opening a diagram and editing it he is getting this error:

Faulting application name: EXCEL.EXE, version: 15.0.5111.1000, time stamp: 0x5c425857 Faulting module name: oart.dll, version: 15.0.5111.1000, time stamp: 0x5c425a13 Exception code: 0xc0000005 Fault offset: 0x00000000005cb2e2 Faulting process ID: 0xb30 Faulting application start time: 0x01d4e94690a56014 Faulting application path: C:\Program Files\Microsoft Office 15\root\office15\EXCEL.EXE Faulting module path: C:\Program Files\Microsoft Office 15\root\office15\oart.dll Report ID: d7ef1281-8e17-4ab8-83c4-28496a46dc6a Faulting package full name: Faulting package-relative application ID:

Any ideas?