" Decoding failed: Syntax error " in magento when updating the product -

i got error when editing , updating weight of product of sku's on backend, , downloadable products,while other simple products gets updated easily. using magento 1.9.1.0 version.the project resembles wordpress , magento integration too. error :

decoding failed: syntax error

and update process gets failed. how can solve this, please me out possible solutions , suggestions.