I can't add certain files to my share and I keep getting this message "Calculated CRC32 does not match the one found in SFV file".

SFV is a file format for storing CRC32 checksums of files in order to be able to verify the integrity of files located in the same folder. SFV's can be used to detect random corruptions in a file. Before hashing and adding a file to the share DC++ automatically checks any file against an .SFV file if one exists in the same directory. This happens for safety reasons (we don't wan't to share corrupted files, right?).

If you get this error message then either your file(s) might be corrupted or the control data in the corresponding .SFV file is outdated or damaged.

The first case is the less frequent one, it can be a sign of file system corruption or storage hardware failure.
The second case is the most probable one; it happens mostly when the files have been altered (mostly by changing the metadata of a media file - eg. the ID3 tag in an .MP3 file) but at the same time the corresponding .SFV file is not updated.

Solution : according to the above either delete corrupted files or recreate the corresponding .SFV file to contain a valid CRC check codes for your files.

There are free tools for create or check the validity of .SFV control files. Google for them. If you use the popular Total Commander software for managing your files it has built-in functions for both checking and creating .SFV.

Alternatively you can delete the .SFV file as well but there is a risk that you'll share corrupted files this way...

More info:
Cyclic Redundancy Check (CRC) http://en.wikipedia.org/wiki/CRC32
Simple File Verification (SFV) http://en.wikipedia.org/wiki/Simple_file_verification