hello, you are most probably missing "customer_note" field within your virtuemart userfields.
please log in to your site in ENGLISH
please navigate to:
Virtuemart -> Configuration -> Shopper fields
search for "note"
you should see something like this:
if not, this is how to create it:
1. click new
2. select type "textarea"
3. length -> default in VM is 2500, but if you need longer length you can use even 25000
4. field name must be exactly "customer_note" without apostrophies
5. default title (translatable) in VM3 is COM_VIRTUEMART_CNOTES_CART
6. rows/cols (ignored by opc) can be 60 columns, 1 row
7. default: leave empty
8. required: NO
9. Show in cart form: YES (this is the only field with TOS checkbox that should be marked as Show in cart form, otherwise a different logic is applied by OPC)
10. Show in Account maintaince: NO
11. Show in Shipping: NO
12. Read-only: NO
13. Published: Yes
14. Field size: 0 (not limited here)
15. Ordering : order as last
If upgrading from VM2.0.x there was no field customer_note at the very early VM2 versions and it was considered as "system field". Upon the upgrade to lastest VM3, it's recommended to create this field in case it's missing.
best regards, stan