Summary:
When you are importing project related information into Web Resource using a CSV file:
 
-Web Resource application would validate the date format on the CSV with that on the browser.
-The language selected in the browser settings decides the date format
-If the date format related to the default language selected on the browser does not match with that on the CSV then we get the following error:
 
 "Unable to convert start date" when I import projects data into Web Resource"
 
Solution:
Check the date format for the dates entered on the CSV file and select a language accordingly in the browser settings.  
 
If the date format on the CSV is dd/mm/yyyy then select English(United Kingdom) in the browser settings.
If the date format on the CSV is mm/dd/yyyy or mm/dd/yy then select English(United States) in the browser settings.
 
-Make sure you restart the browser after changing the language settings.
 
More Information:
 
Use the following steps to change the required language in different browsers:
 
–Internet Explorer 7+: Tools > Internet Options > General (tab) > Languages > Language preference
 
–Firefox 3+: Tools > Options > Content (tab) > Languages > Choose (button)
 
–In Google Chrome: Tools > Options > Under the Bonnet > Languages and Spellchecker settings
 
PS: Make sure the default language that you would like to set is in the top of the list or selected as default language.