What version of MD? What version of OS?
Can you post the beginning (or the whole file) of the error log where it will tell something about what is going on.
Try disconnecting your machine from the network and opening MD. Disable syncing and then connect the network? Just a guess.
(Mac OS) Library/Containers/com.infinitekind.MoneydanceOSX/Data/Library/Application Support/Moneydance/errlog.txt
Press the option key and use the "Go" menu in the finder to access the Library folder.
Or open a finder window, press Shift-Option-G and paste in this path
~/Library/Containers/com.infinitekind.MoneydanceOSX/Data/Library/Application Support/Moneydance (Windows) C:\Users(yourusername).moneydance\errlog.txt