html - Custom Ribbon Button not Executing by Selenium Webdriver -

i writing 1 automation script in unable click on custom ribbon mscrm2011 button below html structure

<li id="contact|norelationship|form|mscrm.form.contact.maintab.exportdata" class="ms-cui-group" unselectable="on"> <span class="ms-cui-groupcontainer" unselectable="on"> <span class="ms-cui-groupbody" unselectable="on"> <span id="contact|norelationship|form|mscrm.form.contact.maintab.exportdata-largemedium" class="ms-cui-layout" unselectable="on"> <span id="contact|norelationship|form|mscrm.form.contact.maintab.exportdata-largemedium-0" class="ms-cui-section" unselectable="on"> <span id="contact|norelationship|form|mscrm.form.contact.maintab.exportdata-largemedium-1" class="ms-cui-section" unselectable="on"> <span id="contact|norelationship|form|mscrm.form.contact.maintab.exportdata-largemedium-1-0" class="ms-cui-row" unselectable="on"> <a id="contact|norelationship|form|fmc.contact.form.button.customer-medium" class="ms-cui-ctl-medium " unselectable="on" href="javascript:;" onclick="return false;" aria-describedby="contact|norelationship|form|fmc.contact.form.button.customer_tooltip" mscui:controltype="button" role="button"> <span class="ms-cui-ctl-iconcontainer" unselectable="on"> <span class=" ms-cui-img-16by16 ms-cui-img-cont-float" unselectable="on"> <img unselectable="on" alt="" src="/%7b635732422790004376%7d/webresources/fmc_/images/hp.fmc.mss360.crm.image.updatecustomer16x16"> </span> </span> <span class="ms-cui-ctl-mediumlabel" unselectable="on">update customer</span> </a> </span> 

i got below exception

  org.openqa.selenium.webdriverexception: [javascript error: "a null" {file: "file:///c:/users/kumarahi/appdata/local/temp/anonymous6568124592565267980webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js" line: 8166}]'[javascript error: "a null" {file: "file:///c:/users/kumarahi/appdata/local/temp/anonymous6568124592565267980webdriver-profile/extensions/fxdriver@googlecode.com/components/command_processor.js" line: 8166}]' when calling method: [nsicommandprocessor::execute] command duration or timeout: 47 milliseconds build info: version: '2.41.0', revision: '3192d8a', time: '2014-03-27 17:18:15' system info: host: 'kumarahi5', ip: '16.185.238.72', os.name: 'windows 7', os.arch: 'amd64', os.version: '6.1', java.version: '1.7.0_79' session id: 279f8847-4a64-4d6c-9ac9-9d703cc8faf4 driver info: org.openqa.selenium.firefox.firefoxdriver capabilities [{platform=xp, acceptsslcerts=true, javascriptenabled=true, cssselectorsenabled=true, databaseenabled=true, browsername=firefox, handlesalerts=true, browserconnectionenabled=true, webstorageenabled=true, nativeevents=false, rotatable=false, locationcontextenabled=true, applicationcacheenabled=true, takesscreenshot=true, version=29.0}]     @ sun.reflect.nativeconstructoraccessorimpl.newinstance0(native method)     @ sun.reflect.nativeconstructoraccessorimpl.newinstance(unknown source)     @ sun.reflect.delegatingconstructoraccessorimpl.newinstance(unknown source)     @ java.lang.reflect.constructor.newinstance(unknown source)     @ org.openqa.selenium.remote.errorhandler.createthrowable(errorhandler.java:193)     @ org.openqa.selenium.remote.errorhandler.throwifresponsefailed(errorhandler.java:145)     @ org.openqa.selenium.remote.remotewebdriver.execute(remotewebdriver.java:595)     @ org.openqa.selenium.remote.remotewebdriver.findelement(remotewebdriver.java:348)     @ org.openqa.selenium.remote.remotewebdriver.findelementbyxpath(remotewebdriver.java:445)     @ org.openqa.selenium.by$byxpath.findelement(by.java:357)     @ org.openqa.selenium.remote.remotewebdriver.findelement(remotewebdriver.java:340)     @ ford_contact2.testwebdrivercontact(ford_contact2.java:117)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method) 

for button have written set of lines none of line working

    driver.findelement(by.cssselector("%7b635731557200004376%7d/webresources/fmc_/images/hp.fmc.mss360.crm.image.updatecustomer16x16"));  driver.findelement(by.cssselector("img.ms-crm-imagestrip-saveandclose_32")).click();  driver.findelement(by.cssselector("span. ms-cui-img-16by16 ms-cui-img-cont-float")).click();  driver.findelement(by.cssselector("a.ms-cui-ctl-medium ")).click();      driver.findelement(by.xpath("//*[@id='contact|norelationship|form|fmc.contact.form.button.customer-medium']/span[1]/span/img']")).click(); 

can not use this:

driver     .findelement(by.id("contact|norelationship|form|fmc.contact.form.button.customer-medium"))     .click();