What this error is telllng you is that you have a missing Jar file (org.apache.commons.httpclient). So double check that this file is indead missing in your userlib. Normally are the Jar files distributed in the modules from the marketplace. If it is not there you could download the Jar from the internet and place it in your userlib. You can find the file for instance here: https://downloads.apache.org/httpcomponents/commons-httpclient/binary/
By reimporting the 3D Viewer module, this issue can be resolved.
Hi Tan Dao,
The error is like, the jar file which you imported is not available in your folder/system.
Reimport the jar file and try once again
It will works!!!!