bids - SSIS Log file, dynamic file path and access denied error -

i have parent package set variable pointing folder want write execution log of package. parent package executes child packages , set value child's variables too.

in child packages package logging stetted , connection string log file built expression:

[user::logfolder] + "\\" + [system::packagename] + ".log" 

but package fail in first step message:

error: 0xc001404b @ child package, log provider "ssis log provider text files": ssis logging provider has failed open log. error code: 0x80070005. acces denied. 

the error happens inside bids. if set path log file statically same path, runs without problems, doesn't seems permissions problem. suggestion on how solve this? in advance.

edit: problem seems happen because [user::logfolder] value obtained parent package, , when package tries open log values have not been passed yet, causing error. there way solve this?

i found answer. records, problem [user::logfolder] value obtained parent package. , child package trying write log before variable value filled, causing error. solved hardcoding log value in package. :-(