uc_dph causes error "Cannot use string offset as an array" while displaying cart

While switched Ubercart 2 DPH support on, accessing cart at example.com/cart causes white screen to appear. After switching displaying errors on, error is shown as follows>

Fatal error: Cannot use string offset as an array in /home/zakaznici/medigrower.cz/www/includes/form.inc on line 990

After switching module off, error disappears.

After some digging I found that there is some issue with variable $form['#attributes']['disabled'] which is possibly not set or set as string instead of an array.

Configuration:
Drupal core 6.19
Ubercart 6.x-2.4
and some other modules (not a complete list):
Ubercart 2 Electronic Waste Recycling Fee support 6.x-1.x-dev (2010-Zář-29)
Ubercart Addresses 6.x-1.0
Ubercart Bought together 6.x-1.0-beta1
Ubercart Bulk Discount 6.x-1.0-beta1
Ubercart Bulk Stock Updater 6.x-1.2
Ubercart Discount Coupons 6.x-1.3
Ubercart Limited Time Offer 6.x-1.1
Ubercart Payment Method Adjustments 6.x-1.0
Ubercart Views 6.x-3.0
UC Add to Cart Tweaks 6.x-1.0-rc1
UC Delivery Date 6.x-1.0-alpha1
UC Gift Certificate 6.x-1.1
UC Gift Order 6.x-1.2
UC Multiprice 6.x-1.0
UC Ordered Products Reports 6.x-1.0-rc1
UC Product Triggers 6.x-1.0-beta3
UC Upsell 6.x-1.21
UC Worldpay 6.x-1.0-rc1
Views Bulk Operations (VBO) 6.x-1.10
Views Slideshow 6.x-2.3

Please do not hesitate to contact me if you need some other informations.