I ran into an unexpected situation during an upgrade that quite honestly, left me a bit baffled. It seems a breaking change was introduced during the CRM 2011 upgrade process.
Some Background
In CRM 4.0, you could open an Entity record with either one of the following URLs:
http://crm2011/Contoso/userdefined/edit.aspx?id=%7bE50B1A7B-1AA2-E211-953E-00155D200507%7d&etc=10010
The difference being using the parameter etn (entity type name) instead of etc (entity type code). Using etn is preferable because it causes fewer issues when migrating from one system to another (development, test, production).
This technique is used extensively in an xRM scenario where you may have additional web pages that use or reference CRM data. It is common to have a screen artifact, like a button, that will open a CRM record when pressed and the URLs listed above are what is used.
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The Issue
It would seem that the etn parameter is no longer supported by the edit.aspx page in CRM 2011 for what appears to be custom entities only. It seems to work fine for out-of-the-box entities.
The Solution
The use of etn is ONLY supported on main.aspx, AND you need to specify the &pagetype=entityrecord parameter, like this:
Further Confusion
I am sure you have noticed, and maybe used, the Copy a Link/Email a Link functionality built into CRM:
This is a very handy feature and I use it all of the time.
Unfortunately, it will return a different URL depending on the entity being used. Standard entities will produce a URL with main.aspx while custom entities will produce edit.aspx.
And again, only main.aspx can use the etn parameter.
Additional Reading
I cover this topic a little more in this article:
Upgrade Your URL Parameter References
and I’ll update that article to reflect this new information.