A required class was missing while "Cell Constraints"

Adding the following in pom.xml resolved the issue:

(Thanks to the solution in https://community.smartbear.com/t5/SoapUI-Open-Source/soapui-maven-plugin-5-4-0-is-not-working/td-p/171251 and documentation in https://www.soapui.org/test-automation/maven/maven-2-x.html )

    <build>
        <plugins>
            <plugin>
                <groupId>com.smartbear.soapui</groupId>
                <artifactId>soapui-maven-plugin</artifactId>
                <version>5.4.0</version>
                    <dependencies>
                        <dependency>
                           <groupId>com.jgoodies</groupId>
                           <artifactId>forms</artifactId>
                           <version>1.2.1</version>
                        </dependency>
                    </dependencies>
            </plugin>
        </plugins>
    </build>

Also, assuming that the following has already been added to settings.xml:

	<pluginRepositories>
		<pluginRepository>
			<id>smartbear-sweden-plugin-repository</id>
			<url>http://www.soapui.org/repository/maven2/</url>
		</pluginRepository>
	</pluginRepositories>

Thanks!