I am not sure whether the client is still actively maintained for current Mac OS versions, but I post this bug just in the hope it might be ;)
I tried the newest version on my macbook with a Raspberry PI client (also running newest version of OS and running the newest version of tightvncserver). The port has been modified, otherwise standard setup.
The session works, but when I close the window, the client crashes, producing the following crash report.
Process: Chicken [437]
Path: /Applications/Chicken.app/Contents/MacOS/Chicken
Identifier: net.sourceforge.chicken
Version: 2.2b2 (2.2b2)
Code Type: X86 (Native)
Parent Process: ??? [1]
Responsible: Chicken [437]
User ID: 501
Date/Time: 2016-01-09 13:39:40.560 +0100
OS Version: Mac OS X 10.10.5 (14F1509)
Report Version: 11
Anonymous UUID: E5D0E1EB-0FE0-E519-C7A6-ABBF54142CEC
Time Awake Since Boot: 40 seconds
Crashed Thread: 0 Dispatch queue: com.apple.main-thread
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x00000000c0045697
VM Regions Near 0xc0045697:
Stack 00000000bf800000-00000000c0000000 [ 8192K] rw-/rwx SM=COW
-->
Submap 00000000ffff0000-00000000ffff1000 [ 4K] r--/r-- SM=PRV process-only VM submap
Application Specific Information:
objc_msgSend() selector name: bounds
Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0 libobjc.A.dylib 0x99f7425f objc_msgSend_stret + 15
1 com.apple.Foundation 0x9b86d76f NSFireTimer + 119
2 com.apple.CoreFoundation 0x9689d006 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION + 22
3 com.apple.CoreFoundation 0x9689cab4 __CFRunLoopDoTimer + 1316
4 com.apple.CoreFoundation 0x9691854f __CFRunLoopDoTimers + 351
5 com.apple.CoreFoundation 0x96854531 __CFRunLoopRun + 2081
6 com.apple.CoreFoundation 0x96853aa6 CFRunLoopRunSpecific + 390
7 com.apple.CoreFoundation 0x9685390b CFRunLoopRunInMode + 123
8 com.apple.HIToolbox 0x934d08f8 RunCurrentEventLoopInMode + 262
9 com.apple.HIToolbox 0x934d0631 ReceiveNextEventCommon + 494
10 com.apple.HIToolbox 0x934d042c _BlockUntilNextEventMatchingListInModeWithFilter + 99
11 com.apple.AppKit 0x927ecb41 _DPSNextEvent + 742
12 com.apple.AppKit 0x927ec1e5 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 350
13 com.apple.AppKit 0x927e0b9c -[NSApplication run] + 907
14 com.apple.AppKit 0x92755fa0 NSApplicationMain + 2082
15 net.sourceforge.chicken 0x00002142 0x1000 + 4418
16 net.sourceforge.chicken 0x00002069 0x1000 + 4201
Thread 1:: Dispatch queue: com.apple.libdispatch-manager
0 libsystem_kernel.dylib 0x9841a8ce kevent64 + 10
1 libdispatch.dylib 0x9c46ace3 _dispatch_mgr_invoke + 245
2 libdispatch.dylib 0x9c46a8c6 _dispatch_mgr_thread + 52
Thread 2:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 3:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 4:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 5:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 6:: com.apple.CFSocket.private
0 libsystem_kernel.dylib 0x9841984e __select + 10
1 com.apple.CoreFoundation 0x968a4b3a __CFSocketManager + 906
2 libsystem_pthread.dylib 0x95aa3c25 _pthread_body + 138
3 libsystem_pthread.dylib 0x95aa3b9b _pthread_start + 162
4 libsystem_pthread.dylib 0x95aa0e32 thread_start + 34
Thread 7:
0 libsystem_kernel.dylib 0x984139ce mach_msg_trap + 10
1 libsystem_kernel.dylib 0x98412a70 mach_msg + 68
2 com.apple.CoreFoundation 0x96854ef6 __CFRunLoopServiceMachPort + 214
3 com.apple.CoreFoundation 0x96854309 __CFRunLoopRun + 1529
4 com.apple.CoreFoundation 0x96853aa6 CFRunLoopRunSpecific + 390
5 com.apple.CoreFoundation 0x9685390b CFRunLoopRunInMode + 123
6 com.apple.AppKit 0x928bc2d0 _NSEventThread + 283
7 libsystem_pthread.dylib 0x95aa3c25 _pthread_body + 138
8 libsystem_pthread.dylib 0x95aa3b9b _pthread_start + 162
9 libsystem_pthread.dylib 0x95aa0e32 thread_start + 34
Thread 8:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 9:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 10:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 11:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 12:
0 libsystem_kernel.dylib 0x98419e6a __workq_kernreturn + 10
1 libsystem_pthread.dylib 0x95aa372a _pthread_wqthread + 939
2 libsystem_pthread.dylib 0x95aa0e0e start_wqthread + 30
Thread 0 crashed with X86 Thread State (32-bit):
eax: 0x004535c0 ebx: 0x002762d0 ecx: 0x93209b8e edx: 0xc0045677
edi: 0x002762d0 esi: 0x02e54180 ebp: 0xbfffd558 esp: 0xbfffd508
ss: 0x00000023 efl: 0x00210206 eip: 0x99f7425f cs: 0x0000001b
ds: 0x00000023 es: 0x00000023 fs: 0x00000000 gs: 0x0000000f
cr2: 0xc0045697
Logical CPU: 6
Error Code: 0x00000004
Trap Number: 14
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