using CSVDE to update proxyAddresses

using CSVDE I've exported a csv file.
I've deleted all columns except for:

DNobjectClass
distinguishedNameproxyAddresses
sAMAccountName


I've revised the contents of the proxyAddresses and now would like to import
(really update) it to modify the contents of the proxyAddresses field.

but the error msg I get is as follows:

csvde -i -f imp.csv
Connecting to "(null)"
Logging in as current user using SSPI
Importing directory from file "imp.csv"
Loading entries.
Add error on line 2: Already Exists
The server side error is "The specified account already exists."
0 entries modified successfully.
An error has occurred in the program
No log files were written.  In order to generate a log file, please
specify the log file path via the -j option.


thank you.