No problem here. Possible cause that comes to mind: using NiCad batteries instead of alkaline. Nicad batteries default voltage might be too low (1.2 volt fully charged); alkaline are 1.5 volt or higher fully charged
So far I have not had a problem with the flash. However, most of the photos I have taken have been landscapes with good lighting so the flash hasn't been used all that much. Sorry I haven't anymore info and good luck.
Do you mean it won't charge at all, or just seems to take too long? In my experience cameras that run on AA cells, especially alkalines (or worse, carbon zinc), take longer to recharge the flash than lithium ion because the batteries can't deliver as much current. IF you have fresh batteries and the flash won't charge at all (assuming flash is enabled), then it sounds like a defect with the camera.
I have used NiMh and rechargeable batteries with no problem with mine, although most of my shots are in bright, existing light. There are a couple of settings that will prevent the flash from functioning. The flash will not work in Discrete Mode or the No Flash Mode. There may be other settings also. Check the manual.