I do not know how the code:
<!--START SIMPLEVIEWER EMBED -->
... is being introduced to the beginning of your 'simpleviewer.js' file (if this is, indeed, the file you are referring to) but a solution should be to just upload a fresh copy of the 'svcore' folder (from your SimpleViewer-Pro download zip package) to your web server (replacing your gallery's existing version). If you are in any doubt as to whether or not the 'svcore' folder on your web server is being overwritten, delete the old version from your web server first before uploading the new version in its place.
If the file you are referring to is not the 'simpleviewer.js' file, then you seem to have part of the 'simpleviewer.js' file in your HTML page (which is just as strange) and a style attribute in your script tag which should not be there. In any case, there is a problem and if re-uploading the 'svcore' folder does not help, then please post the URL to your gallery's web page so that I can take a look at the problem for myself and hopefully help further.
SimpleViewer Support Team