I had also received the “Record is Unavailable” error.
I had done many customizations to the Order Entity on one CRM 2011 virtual server while my customer got their hardware ready for MS CRM 2011.
When their server had CRM 2011 installed I imported the solution.
All the entities except Orders would allow me to Add New/Save.
After reviewing my code I remembered that I had Jscript which did a Lookup to the PriceList. This requires a GUID value in the code.
The GUID was for the Development site SQL database tables.
Once I changed the GUID to the correct value for the Live CRM installation, the error went away.
Hope this helps others resolve their problems.
Valerie Lingen