problems with Command-line parser?
The problem is most likely in the way your shell is interpretting the command line which can be compounded if the shell is being called from a scripting language like PHP. Next up we'll need to know if your calling from a scripting language or a shell. Which shell are you using? Which operating system? Which version of ImageMagick?
In ImageMagick 6.2.6-7 Beta we added a new log statement to display the actual command line being passed to the convert program to make debugging situations like yours easier. All you need to do is add -debug configure to the command line to get this information (and of course use ImageMagick 6.2.6-7 or above). The patch will be available by tommorrow.