Many servers run on Unix or Linux; these systems are completely intolerant of differences in uppercase and lowercase file names. If you have uploaded, say, ptviewerBeanInfo.class through a ftp program that automatically changes all filenames to lowercase, the name of the file on the server will then be ptviewerbeaninfo.class, and browsers will not be able to find the file if their code specifies the original name which includes uppercase characters.
I personally am careful always to name all files (and extensions) in lowercase to avoid this type of problem. However, the java applets and ActiveX scripts are programmed to summon files with the original uppercase characters. So it is imperative that you make sure that the files summoned by applets and various scripts have the exact same uppercase and lowercase characters in their names once they are uploaded to the server. You can use your FTP program's rename function to correct any discrepancies.
If that doesn't correct the problem, it must be something else...
I hope this helps