The names of the sprites are case sensitive, and some lump editors such as XWE will make everything automatically upper-case unless you tell it not to in the options. Check the sprites near the bottom, SILVa1, SILVb1, etc, and if the frame letters are upper-case instead of like the examples above, change them back.
If that turns out not to be the problem, you should probably upload the wad so others can take a closer look to figure out what's wrong.