I executed code in my target board overnight under control of Keil uVision 4.54 Debugger. In the morning code wasn't running. It was stopped in the first instruction of main(). uVision command window displayed "internal DLL error". My guess is there isn't problem with my software or target board. Maybe due to power surge or some other reason uVision went into strange mode.
Why is "internal DLL error" occurring ?
Often a connectivity issue with the JTAG/Debug pod and the system. The board could have reset/repowered, or gone into a low power state.
"Internal DLL" usually just refers to one that's part of the Keil package rather than a Windows system one, and represents a general error/failure which is hard to pass specifically to the user interface.