Suggestions by @addison74

Author: fballiano

app/code/core/Mage/Contacts/controllers/IndexController.php

@@ -76,7 +76,7 @@ public function postAction()
                 }
 
                 if ($error) {
-                    Mage::throwException($this->__('Unable to submit your request. Please, try again later'));
+                    Mage::throwException($this->__('Unable to submit your request. Please try again later'));
                 }
                 $mailTemplate = Mage::getModel('core/email_template');
                 /** @var Mage_Core_Model_Email_Template $mailTemplate */
@@ -91,7 +91,7 @@ public function postAction()
                     );
 
                 if (!$mailTemplate->getSentSuccess()) {
-                    Mage::throwException($this->__('Unable to submit your request. Please, try again later'));
+                    Mage::throwException($this->__('Unable to submit your request. Please try again later'));
                 }
 
                 $translate->setTranslateInline(true);
@@ -106,7 +106,7 @@ public function postAction()
                 Mage::getSingleton('customer/session')->addError($e->getMessage());
             } catch (Throwable $e) {
                 Mage::logException($e);
-                Mage::getSingleton('customer/session')->addError($this->__('Unable to submit your request. Please, try again later'));
+                Mage::getSingleton('customer/session')->addError($this->__('Unable to submit your request. Please try again later'));
                 $this->_redirect('*/*/');
                 return;
             }

app/locale/en_US/Mage_Contacts.csv

@@ -15,5 +15,5 @@
 "Send Emails To","Send Emails To"
 "Submit","Submit"
 "Telephone","Telephone"
-"Unable to submit your request. Please, try again later","Unable to submit your request. Please, try again later."
+"Unable to submit your request. Please try again later","Unable to submit your request. Please try again later."
 "Your inquiry was submitted and will be responded to as soon as possible. Thank you for contacting us.","Your inquiry was submitted and will be responded to as soon as possible. Thank you for contacting us."