Upgraded Virtuemart from 2.0.18 to version 2.0.24 using the Extension Manager (Installed VM 2.0.24 zip file)

But I found that an error on the product pages of the slave sites only. Also, the custom fields were not showing on the page. This was the error:

getProductCustomsFieldCart Unknown column 'show_title' in 'field list' SQL=
SELECT C.`virtuemart_custom_id`, `custom_title`, `show_title`
, C.`custom_value`,`custom_field_desc` ,`custom_tip`
,`field_type`,field.`virtuemart_customfield_id`,`is_hidden`
FROM `medphys_virtuemart_customs` AS C
LEFT JOIN `medphys_virtuemart_product_customfields` AS field ON C.`virtuemart_custom_id` = field.`virtuemart_custom_id`
Where `virtuemart_product_id` =596 and `field_type` != "G"
and `field_type` != "R"
and `field_type` != "Z"
and is_cart_attribute = 1
group by virtuemart_custom_id
ORDER BY field.`ordering`

I looked at the database via phpMyAdmin and saw that the Virtuemart SQL views for the slave sites had not been updated along with the master tables with this custom fields column.

SO, I used the Jms tools menu to uninstall VM and then redo the 'Share with Master' option for EACH subsite.This fixed the issue. the views were updated by this process.

So next time I upgrade VM, I need to remember to subsequently uninstall and then re-share VM on each site to keep the views updated. I didn't know this, although it may have been in some instructions somewhere. Thought I'd post in case someone else had this issue.

When you share the content of an extension (ie. VirtueMart), JMS use the MySQL VIEWS to make the sharing.

Unfortunatelly, when the MySQL table structure is modified, MySQL does not reflect those changes into the VIEWS.
You have to drop manually the views and rebuilt.
Rebuild the views is easy.
You just have to go in JMS and open the slave site definition that you re-save.
This will rebuild all the missing tables (or views) in this case.