The good news is the CRM UI only provides user friendly error messages. The bad news is that this does not give you a lot of information to go on when troubleshooting a problem.
In order to see more details about an error when you are troubleshooting you can turn "DevErrors" on.
You can do this by editing the web.config file.
The web.config file will be located in one of two places:
1) If you installed to the default website it will be in %system root%\inetpub\wwwroot
2) If you installed to a new web site it will be in %system root%\program files\microsoft dynamics crm\crmweb
Open the web.config file with notepad and do a find for "DevErrors". You will find a section in the web.config file that looks like this:
<add key="DevErrros" value="Off" /> change the value to "On" as follows: <add key="DevErrros" value="On" />
Save the file and from the commandline run iisrest.
DevErrors are turned on and when an error is encountered in CRM you will see the full error details.
Don't forget to turn this off when you are done!