> After some surfing through several forums we detected that problems
> could be among:
> 1) incompatibility of clients (gds32.dll, fbclient.dll, etc.)

No way.

> 2) incompatibility of UDFs (i.e.: rfunc)

Most probably.

> 3) Network disconnection of some clients (errors 104, 32, etc. in the
> log).

No way

> 4) Incompatibility of components used in the source code (Zeos,
> Intersol, IProvider, etc.)

Absolutely no way.

> 5) Queries that are restricted from FB 2.0 (table alias, etc.)

No way.

> 6) Linux rights over some files or folders? (errors while writing to
> FDB datafiles).

Very unlikely.

> 7) Any other I forget?

Hardware faults. The fact that they appear at the same time with
migration may be just a coincident.

SY, SD.