Error when upgrading sandbox solution

The URL '_catalogs/solutions/mysolutions.wsp' is invalid. It may refer to a nonexistent file or folder, or refer to a valid file of folder that is not in the current Web.

I encountered this error when trying to upgrade a sandbox solution in Sharepoint 2010.

Solved:
The problem was due to a feature template xml having a wrong namespace given to the assembly name for the feature receiver attributes. I corrected the namespace problem and the upgrade started working fine.
The corrected section of the feature.template.xml goes like this.
<UpgradeActions ReceiverAssembly="HelloWorld, Version=1.0.0.0, Culture=neutral, PublicKeyToken=b2135059549c7590"
ReceiverClass="HelloWorld.Features.HelloWorldFeature.HelloWorldFeatureEventReceiver">