You can ignore that error. But when the import process finish probably you will get:
Plugin execution not covered by lifecycle configuration:
org.apache.maven.plugins:maven-antrun-plugin:1.3:run (execution:
generate-sources, phase: generate-sources)
If so, reason is that your current configuration doesn't support maven-antrun. You can find a related question here: How to solve "Plugin execution not covered by lifecycle configuration" for Spring Data Maven Builds
An explanation of the problem can be found here: http://wiki.eclipse.org/M2E_plugin_execution_not_covered
Easy way to solve? Adding the next block of code to your pom.xml:
<pluginManagement>
<plugins>
<plugin>
<groupId>org.eclipse.m2e</groupId>
<artifactId>lifecycle-mapping</artifactId>
<version>1.0.0</version>
<configuration>
<lifecycleMappingMetadata>
<pluginExecutions>
<pluginExecution>
<pluginExecutionFilter>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-antrun-plugin</artifactId>
<versionRange>[1.0.0,)</versionRange>
<goals>
<goal>run</goal>
</goals>
</pluginExecutionFilter>
<action>
<execute>
<runOnIncremental>false</runOnIncremental>
</execute>
</action>
</pluginExecution>
</pluginExecutions>
</lifecycleMappingMetadata>
</configuration>
</plugin>
</plugins>
</pluginManagement>
After some usual update Maven project configuration, clear and rebuild all, pom problem disappear.
But then you will get probably some error about missing classes. You must download the protoc binary and execute it for all the .proto files you can find on your sources directory. Example:
protoc --java_out=src/main/java -I../src ..\ src\google\protobuf\descriptor.proto