Platform is Trisquel 7, an Unbuntu derivative. Motherboard is an Intel D865GLC with 3GB of memory, recently upgraded to 4GB (moved to another identical motherboard).

Emails were retrieved from a network attached storage drive, to which the profile had been uploaded from a WinXP, SP3 installation running Thunderbird email client.

Emails that are mostly irretrievable are from a folder containing ca. 13,500 emails. These are all OK in the original installation.  Total about 800MB. There were many duplicate emails which KMail atttempted to remove.

I can repeat the transfer process if need be and if some trials are anticipated.

KMail 4.13.3 is the version; installed from the Trisquel repository with apt-get.

Here is the complete error message, which I get every time I try to open an email in the folder list and the loading fails:
"Unable to fetch item from backend (collection 0): Unable to retrieve item from resource: Invalid item retrieved"
 This is what I get for about 95% of the emails that I have retrieved from various sources. No other error messages are apparent, even with dmesg in Terminal.

One much larger folder (several GB) will not open at all.


Reproducible: Always

Steps to Reproduce:
1.Load various email profiles to NAS - all in one folder;
2.Retrieve with KMail; KMail grabs every profile in one "go;"
3.KMail organizes everything automatically in Trisquel 7 installation;
4.Attempts to read any email in most folder gives error message; 
5.Most messages are irretrievable; some folders are OK.

Actual Results:  
Shall I erase all 10GB in the KMail installation and start over ? This is a days-long process.
I'm reluctant to stick my finger in the piranha tank again anytime soon.