[Typo3] Fatal error: Only variables can be passed by reference

[racco]

Hello!

I do not know why, but since a while (I cannot say since when exactly) 
my site generates this mysterious error after submitting any form 
displayed using MailFormPlus ext.

The error is as follows:
Fatal error: Only variables can be passed by reference in 
.../t3lib/class.t3lib_db.php on line 980

What is important, all data from form gets stored correctly


Could you please give me any hints about this?
On my server I have php version 3.3x and it is there since long time and 
before everything worked just fine


looking forward to getting some support


greetings
racco