I had the same problem with B737NGX. Simply delete the FSIUPC.INI. When I opened it again it creates another and solve the problem!

 

 

FSUIPC.ini was the problem!

 

Please click "Mark Solved" on the post that gave you the information to solve your problem.  This helps people who may run across this problem in the future, and it also helps guys like me who are scouring the forum to help people - it lets me know it's been solved and to continue looking at other threads.

 

Thanks!

Im having this exact same issue! My autopilot and a/t goes into CLB mode, but my aircraft picthes 5 degrees down and wont climb! Going to try deleting my FSUIPC.ini file..see it that works