upgrade 3.7.4 to 3.8.0 beta4

[learncity]

Hello
I try upgrade my vB from 3.7.4 to 3.8.0 beta 4 but in the fifth level of upgrade this error is coming up

Catchable fatal error: Object of class vB_Database could not be converted to string in /home/........./public_html/forum/includes/class_core.php(998) : eval()'d code on line 7

how can I fix that problem?
tnx

 

[AvADeO]

Wrong place mate.