When wiping the unused disk space (the free space) on a drive or scrambling the deleted files and folders properties, east-tec Eraser creates a series of temporary files (.WIP files) in the root folder and fills the space there until there is no free space left on the drive. To solve the issue all you need to do is to start east-tec Eraser, let it finish the erasing process and the temporary files (created by Eraser) will be deleted.
If the process is somehow interrupted, the WIP files will not be deleted and you will need to remove them manually. To locate them in Windows Explorer is very easy. Go to Computer and click on the letter of the drive from which the files were erased from (it's usually Local Disk (C:) and look for files with the extension .wip. You should find as many wip files there as many files got erased. Then simply select them and use the SHIFT + DEL key combination to delete them.
NOTE: Even if you miss to erase these wip files manually, there is no danger of sensitive information being recovered from them. They contain random characters and that is not sensitive information. These temporary files are only used as a way to completely get rid of previously deleted data. This way, even if these files (with random data) can be recovered, they don't offer any clues about what was on your hard drive, or what you have used to erase this data (e.g. east-tec Eraser).