Following are the general error you will observer if you have missed a step:

Error: Load unsafe content or Please reload your browser message (even after refreshing browser window)
Reason: Occasionally your Celoxis configuration URL may not have 'https' that may cause this issue. Please verify that your configuration URL has 'https://'. Login in as administrator into your Salesforce.com account.
Go to Setup > Installed Package. Click on 'Configure' link next to "Celoxis". In the URL field, change the http to https. Save changes. Now try accessing your Salesforce Opportunity page.
Error: Oops, there was an error rendering Force.com Canvas application [CeloxisApp].
You don't have permissions to view application with namespace [celoxis] and API name [CeloxisApp]. Click to configure
Solution: When accessing an Opportunity, in the Celoxis section you see this. To resolve
1. Go to Administration Setup > Manage Apps > Connected Apps > Click on the Celoxis App.
2. On the new page, scroll down to the Profiles section and click on Manage Profiles button.
3. Select the profiles you want to enable access for Celoxis app and click on Save.
  You should now see the Celoxis section.
Issue: You see the Celoxis section on the opportunity page, but its grayed out.
Solution: You need to increase the Height in Pixels of the Celoxis section to min 600 on the opportunity layout page.
Error: SSL protocol error on app layout page in the Celoxis layout.
Solution: When configuring Celoxis app, check that the Celoxis URL is entered correctly with the correct protocol (use: https://) and correct portnumber.
Issue: The section to create project in Celoxis is not visible on the Opportunity page.
Solution: The Opportunity layout page either not configured correctly OR the user's profile is not selected for the layout created for Celoxis (For enterprise and higher editions).
Issue: The Celoxis Salesforce App might not be visible properly using an IE browser.
Solution: It is recommended to use one of the supported versions of IE and set the options mentioned in the link below:
https://help.salesforce.com/apex/HTViewHelpDoc?id=getstart_browser_ie.htm&language=en_US#getstart_browser_ie

Browser not supported