I have a PROFIBUS DP network with ProSoft PROFIBUS DP Master solution that appears to be operating normally (no bus faults, slaves report "OK"), but I am unable to control my devices. What

Many things can result in these symptoms.  One of the most common causes is that not all slave manufacturers use a standard byte order.  It is very possible that when you think you're sending a value of "1" to a slave's bit address 0, you may be sending a "1" to the slave's bit address 8. 

Enabling the Swap Input/Output Byte parameter would resolve the issue in this case.