I just wanted to add to this thread as its related and the thread isnt too old..so a search will throw this up.
Most errors in wad manager, if you can load the program and list the SD card wad files are likely to be with cIOS's that are not working with wad manager. Either they are not installed properly or something else is preventing it working (like stubbed) or you need an updated IOS.
an example is in the posts above and another is ERROR (ret= -1029) on 4.2 softmodded wii
This occurs when trying to run wad managers 1.4-1.6 in IOS249/250, but it will usually work from IOS236
other errors are:
ERROR (ret= -1017)
ERROR (ret= -1022)
ERROR (ret= -1035)
ERROR (ret= -2011) -- bad wad file or need IOS updating.
ERROR (ret= -4100) -- bad wad file??
In some cases the wad file may be corrupt/injected incorrectly, other areas could be due to insufficient memory but usually an IOS problem.