How did you install it?
If you used slackware 10.0 packages (from linuxpackages for example) then the problem may be that the package was compiled with a different set of libraries (or ones with different names
) than what is currently on your system. You will need to either wait for a 10.1 package to show up, or roll your own.
If you compiled from source, then you may need to add extra parameters to the ./configure command to tell it where to look. Read the output of ./configure --help for a list of options.
Thats all I have to add as I do not use Opera.
Good luck.