same issue here.
When I enter the data for new owncloud accounts, accountsd crashes:
Bad to hear that other caldav providers are affected, so it must be the fault of the Address book sync dialog.
process: accountsd [1891]
Path: /System/Library/Frameworks/Accounts.framework/Versions/A/Support/accountsd
Identifier: accountsd
Version: 113 (113)
Code Type: X86-64 (Native)
Parent Process: ??? [1]
Responsible: accountsd [1891]
User ID: 501
Date/Time: 2015-10-12 22:30:25.811 +0200
OS Version: Mac OS X 10.11 (15A284)
Report Version: 11
Anonymous UUID: DF869F1B-466C-AC13-8BA5-25CD7866E674
Time Awake Since Boot: 15000 seconds
System Integrity Protection: enabled
Crashed Thread: 3 Dispatch queue: com.apple.NSXPCConnection.user.1865
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: EXC_I386_GPFLT
Exception Note: EXC_CORPSE_NOTIFY
Application Specific Information:
objc_msgSend() selector name: initWithCoder:
Thread 0:: Dispatch queue: com.apple.main-thread
0 libsystem_kernel.dylib 0x00007fff8c05ec96 mach_msg_trap + 10
1 libsystem_kernel.dylib 0x00007fff8c05e0d7 mach_msg + 55
2 com.apple.CoreFoundation 0x00007fff93167024 __CFRunLoopServiceMachPort + 212
3 com.apple.CoreFoundation 0x00007fff931664ec __CFRunLoopRun + 1356
4 com.apple.CoreFoundation 0x00007fff93165d38 CFRunLoopRunSpecific + 296
5 accountsd 0x0000000106800a12 0x106800000 + 2578
6 libdyld.dylib 0x00007fff9ae7d5ad start + 1
Thread 1:
0 libsystem_kernel.dylib 0x00007fff8c06478a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x00007fff9b02b58c _pthread_wqthread + 1283
2 libsystem_pthread.dylib 0x00007fff9b029375 start_wqthread + 13
Thread 2:: Dispatch queue: com.apple.libdispatch-manager
0 libsystem_kernel.dylib 0x00007fff8c0650a2 kevent_qos + 10
1 libdispatch.dylib 0x00007fff98b8a1ad _dispatch_mgr_invoke + 216
2 libdispatch.dylib 0x00007fff98b89e15 _dispatch_mgr_thread + 52