Setup asks for a runtime
Install Microsoft .NET Desktop Runtime 8 x64 from the official download opened by setup. Finish that installation and run the application setup again. A different .NET runtime type may not provide the desktop components.
Export is not available
For one file, select Cut MP3 and select a valid audio clip. Join MP3 needs at least two valid clips. Finish importing before starting an export.
Check that the selected range contains audio time. If you requested Lossless Copy after trimming or adding an effect, use Smart or Studio processing instead.
A file will not load or save
Try a short, known-good local audio file. A file extension alone does not prove that the content is readable, and protected or damaged files may fail to open.
Choose a writable local output location and close another application that may have the target file locked. The program will not overwrite an input file.
The volume changes at a join
Open Advanced and consider loudness normalization for a sequence recorded at different levels. Listen across the join afterward; normalization does not repair distortion or clipped speech already present in a source.
Report a reproducible problem
Email support@freemp3cutterjoiner.com with Windows version, application version, input and output formats, the steps taken, and the error text. A short non-sensitive example can help reproduce the issue.