Illegal Data format in DB for datalog

Good afternoon to all, 

I would like to ask a question about datalog to 1200 because I have some troubles.

I have a FB (FB15 in picture 1) where inside i wrote the logic and where there is the datalog blocks (open, create, write, close) as local instances.

I wanted to pass the DB to log from ouside, so I feed the write FB with a Variant in/out variable. (Picture 2, DB_Sorgente variable) 

The detail of DB is in picture 3. I have some UDT that simple define a DINT and a LREAL.

Mi problem is that when I trig the Datalog create, I get 8C51 error that mean incompatible data in datalog to store.

I tried with a simple DB with a bunch of heterogeneus var and is working fine that time. Only when I try to add a UDT things goes wrong.

Do you have any Idea why this happen? I tried to search along manuals but I dindt able to find any valuable solution.

Thankyou very much for your help.

Luca V.

Goodmorning Huggy.

Thankyou for your explanation. 

I misunderstood help statement that says:

"Tipo di dati non consentito nel parametro DATA / struttura di dati non utilizzabile."

, however the italian translation is a bit ambiguous because it says "your structure cannot be used, and don't state structures cannot be used". Finally, I was on the idea that UDT was the problem, but I was searching an  expert confirmation.

In other projects, where large data structures was used, I passed the DB by pointer, let say P#DB24.DBX0.0 WORD 250, this let me save data regardless on their format and number ( I saw maximum amount of items/tags per datalog session is 255)

However this mean that in datalog file the original structure is lost (just formatted by words array in this case) and need a sort of decoder to get back your data. (I do in .NET).

Thankyou for your advice. The thing I would to avoid is to make FB15 dependent of the actual application, because is part of a library...

Maybe I ask too much if there is a magic standard instruction that take out UDT and preserve data format ?

Or maybe is better do the conversion using an FC in the Main and preserve the library datalog FB.