Do not hesitate to use the GSplit forum to post your questions. First, have a look to the existing threads: maybe your question already got an answer.

• GSplit won't recognize a DVD-RW disk; I get a "cannot access destination folder" error. Is this a known problem?

 GSplit works with CD and DVD Recordable / Rewritable drives if a proper device driver is installed and configured with your drive. The driver should make the CD/DVD behave like a large floppy disk. Check with your CD/DVD documentation.
To see if GSplit can work with your drive, try to copy some files from your hard disk to the drive using Windows Explorer. If Windows Explorer can copy files to the drive, GSplit can too.

• When using GUnite, I receive a fatal error saying this: "System Error. Code 23 Data Error (cyclic Redundancy check)"

This error is not due to GUnite itself, but it comes from Windows. It is a problem related to hardware: this error occurs generally when trying to read data from a damaged CD or DVD.

• I receive this error: "System Error. Code: 112. There is not enough space on the disk", although this is not the case.

Volumes with a FAT32 partition only accept files up to 4 GB. Be sure that the destination drive is formatted with the NTFS file system. 
The NTFS file system does not have the 4-GB limitation on file size.