Unable to locate Attribute with the the given name [X] on this ManagedType [Y]

Question

I have encountered many posts on the Internet about this specific error, and in all of them the programmer is using the wrong case on the attribute, but I don't think that's the case in my situation (or it is, and I simply don't know what to use, in which case your reply is appreciated). I have the following domain classes:

The 'WallpaperTag' class (containing the link between the 'Wallpaper' and 'Tagname' class, so multiple tags can be applied to a single wallpaper and vice versa):

class WallpaperTag implements Serializable {
    Wallpaper wallpaper
    Tagname tagname

    static mapping = {
        if (Environment.current != Environment.TEST) {
            table name: 'JWS_JWS_WALLPAPERS_TAGS', schema: 'jws'
            id composite: ['wallpaper', 'tagname']

            columns {
                wallpaper column: 'JWS_JWS_WAL_KEY', sqlType: 'INTEGER', length: 11, lazy: false
                tagname   column: 'JWS_JWS_TGN_KEY', sqlType: 'INTEGER', length: 11, lazy: false
            }
        }

        version(false)
    }

    static constraints = {
        wallpaper nullable: false, blank: false, maxSize: 11
        tagname   nullable: false, blank: false, maxSize: 11
    }

    WallpaperTag(Wallpaper wallpaper, Tagname tagname) {
        this.wallpaper = wallpaper
        this.tagname = tagname
    }
}

The 'Tagname' class (containing the actual tag names that can be applied to a Wallpaper)

class Tagname {
    String name
    Purity purity

    static mapping = {
        if (Environment.current != Environment.TEST) {
            table name: 'JWS_JWS_TAGNAMES', schema: 'jws'
            id column: 'key', sqlType: 'INTEGER', generator: 'identity'
        }

        name   column: 'NAME',            sqlType: 'VARCHAR', length: 255
        purity column: 'JWS_JWS_PUR_KEY', sqlType: 'INTEGER'

        version(false)
    }

    static constraints = {
        name   nullable: false, blank: false
        purity nullable: false, blank: false
    }

    Tagname(String name, Purity purity) {
        this.name = name
        this.purity = purity
    }
}

Whenever I try to execute the following Hibernate query, the error occurs (error triggers on the "'tagname' {" line):

List<WallpaperTag> wallpaper_tags = (List<WallpaperTag>) WallpaperTag.createCriteria().list {
    'tagname' {
        inList('name', tags)
    }
}

The error message itself:

Caused by: java.lang.IllegalArgumentException: Unable to locate Attribute  with the the given name [tagname] on this ManagedType [org.grails.guides.WallpaperTag]

Things I have tried to fix this issue:

1. Refactored the 'Tagname' class to 'TagName' (capital N, to make it camelcase)
2. Refactored the 'tagname' attribute to 'tagName' (capital N, to make it camelcase).
3. Renamed the mapped column name from 'JWS_JWS_TGN_KEY' to 'JWSJWSTGNKEY' (I know this probably wasn't the issue, but still worth trying).

If anyone knows what the issue might be, your knowledge would be appreciated!