I've also been experiencing this problem (with Entropy template). Turning off the Joomla cache removes the error for me too, but not really an ideal solution!
Try Global Configuration:System:Cache Settings:On - Conservative caching.
After making that change, purge all of your old cache files.
When I was running the Progressive caching, I was getting the line 42 error. My cache was also getting corrupted regularly and my pages would be a mess until I cleared the caches. Going to Conservative caching appears to have solved the line 42 error on my mobile device (blackberry bold) and it hasn't corrupted itself.... yet.
I'm running Modulus 1.6.2 on Joomla 1.7.1 with Gantry 3.2.11 and Gantry Cache = On; Gantry GZipper = On
Same Problem for me (Paradox 1.6.1)..
I had Joomla Conservative Caching on.. was gettng the error consistently.
When I turned off Joomla Caching the mobile version of the Site came through finally on the android. It is not an actively used site right now but it seems this is a fundamental issue in Gantry that should be resolved.
Great to see the thread on this and great to see folks working on it. Not sure that I was hearing from Gantry/RT folks through the thread or not... In any case. long term solution seems in order.
Regarding Gantry/Caching/Mobile " In any case. long term solution seems in order."
Yes please, RT, any plans to address this? Mobile Joomla is filling the gap for me, but not the best solution. My wordpress sites do much better with mobile devices.
Might be of no importance... I have three sites. The one on the Root of my shared hosting system works with IPhone, the two others in subdirectories don't. The settings are identical. All are using Momentum 1.2 with Joomla 1.7.2
I get the same error using Hybrid with J1.7 - come on RT Suport - any ideas? Fatal error: Cannot access protected property JParameter::$_raw in /mysite/public_html/libraries/gantry/facets/menu/gantrymenu.class.php on line 42
Tim