s7-300 compiling error

Hello!

I have encountered strange error while compiling step7 project for s7-300.
this error occurs in DataBlock compiling.
compiler says

"W Ln 000007 Col 006: No valid offline ASCII type description found for called or adressed block UDT1"
and
"E Ln 000007 Col 006: No PLC type description found for called or addressed block UDT 1"

What does it mean ? should there be any PLC description in DB connected with counter module?

The DB is referencing UDT1 and the definition for it is missing.

You are right, thank you very much!
Do you know maybe if it is possible to reconstruct UDT1 when I know DataBlock associated with it?
I mean are the UDT1 references in DB somehow different than the "standard" DB entries, so I can recreate UDT1 ?
My task is to complete program downloaded from PLC.
In this project counter FM350-2 has been used, and DB associated with counter calls UDT1 so its probably for handling 64bit numbers.