why can't new the Topic attribute map in Lead's account_originating_lead relationship?

Problem :

I want the "Topic" data to automatically pull over from the lead record when the lead is converted to an account. I created a new attribute called "Originating topic" on Account form (type, format, and length are all same as Lead's topic attribute). And then try to create a mapping for it in Lead's account_originating_lead relationship, but it always pops up an error stating this attribute map is invalid. A vaild attribute map must meet these requirements: - The data type must match. - The length of the target attribute cannot be shorter than the source attribute. ....
I am sure the map meets those requirements.  And I created a map for another attribute, it works.
so I was wondering why the map for "topic" cannot be created. how do I solve this?
Appricate any advice.

Soln :
Both the Source and Target fields have to be published on the forms for their entities.  But you know what?  That's not enough.  Why?  Because CRM is lying to you .  Open your Metadata Browser to the following location, and tell me what you see for the "Subject" field:
http://<crm server>/<org>/sdk/mdbrowser/entity.aspx?entity=lead
The length is different, isn't it?  Why?  Because CRM is superior to you in every way, and it wants to make you feel like a small boy in the middle of a Civil War.  Apparently there's a mismatch in what the Metadata knows, and what the customization UI represents.  The fix?  Simply increase your target attribute to the length identified by the Metadata.
The mind-trip?  Before you create the mapping, change the target attribute back to the original value that you first believed was right.  It works.  The secret?  Occam's Razor gives us the best answer:  it's magic.

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http://social.microsoft.com/Forums/en-US/crmdevelopment/thread/deaa3d55-3e04-4411-8450-80d35e03eb9b