Manual upgrade 1.4.6.2 to 1.6 fail error 34

[wiros]

I did a manual upgrade from prestastore. I got the following errors:

 

<action result="fail" error="34">

…

<request result="fail" sqlfile="1.5.0.0">

<sqlQuery>

<![CDATA[

UPDATE ps_stock_mvt sm SET sm.id_stock = IFNULL(( SELECT IFNULL(s.id_stock, 0) FROM ps_stock s WHERE s.id_product = sm.id_product AND s.id_product_attribute = sm.id_product_attribute ORDER BY s.id_shop ), 0)

]]>

</sqlQuery>

<sqlMsgError>

<![CDATA[ MySQL server has gone away ]]>

</sqlMsgError>

<sqlNumberError>

<![CDATA[ 2006 ]]>

</sqlNumberError>

</request>

....

<request result="fail" sqlfile="1.6.1.0">

<sqlQuery>

<![CDATA[ ALTER TABLE `ps_shop` DROP KEY `id_shop_group` ]]>

</sqlQuery>

<sqlMsgError>

<![CDATA[

Can't DROP 'id_shop_group'; check that column/key exists

]]>

</sqlMsgError>

<sqlNumberError>

<![CDATA[ 1091 ]]>

</sqlNumberError>

</request>

 

Can someone give advise how to continue?