Hello, I have a simple OpenGL program that is using Boost Threads and I had it working fine under Boost 1.34. I have switched to 1.36 for some of the newer mutex locking functionality and everything works fine, but.. I keep getting an invalid memory access error. My program will run fine if i skip past the offending call. Wondering if anyone has any ideas? The offending call happens when the rendering thread is created. The call stack is as follows: Access in invalid memory in process: solarsystemT.exe(4056) - :\development\boost_1_36_0\boost/thread/win32/once.hpp#125 Attempt to access 4 byte(s) at 0x00417084. 0x00411056 - E:\development\boost_1_36_0\boost/thread/win32/once.hpp#125 0x0041137B - E:\development\boost_1_36_0\libs\thread\src\win32\thread.cpp#44 0x00411A61 - E:\development\boost_1_36_0\libs\thread\src\win32\thread.cpp#151 The memory that boost::call_once is accessing is current_thread_tls_init_flag created earlier by boost::once_flag current_thread_tls_init_flag=BOOST_ONCE_INIT; I can see that this flag was created and initialized to zero. Thank you for any insight. Stephen Kierzewski