1) The "WIC" in "WIC Error: 0x80070057..." stands for "Windows Imaging Component" ( https://en.wikipedia.org/wiki/Windows_Imaging_Component
), a standard Windows operating system component that applications, including Inquisit, use to render images on-screen.
First off, make sure all systems in question have the latest WIC installed. WIC updates come via the normal Windows Updates, so make sure all machines are up to date.
Different Windows versions use different WIC versions, i.e. Windows XP will use an older version than, say, Windows 7, and not every newer release is available for older Windows versions. Now, especially older versions of WIC react really badly to certain issues with image files, particularly invalid metadata embedded in the image files. Other encoding issues with the image can also cause trouble (e.g. using CMYK instead of RGB colorspace). Something along those lines is likely what's ultimately causing the problem. If you remove all the metadata from the image files used in your study, it should run fine. You can use a program like IrfanView to do this in bulk for all image files or you can open them with a simple Windows image editor (MS Paint will do) and simply re-save them.
2) For WAV files to be cross-platform compatible, make sure they're encoded as 16-bit PCM WAV files. The Windows API the <sound> element maps to does not accept 32-bit WAV files. Alternatively, you can try using the <video> element instread of <sound> to play your audio files.
What the specific issues with your files are, I cannot say since you didn't provide them along with the script.