Numbers spreadsheet can't be imported I have a spreadsheet I have been updating in IOS Numbers for several months and I sometimes update it with OSX Numbers

However when I did a recent update in OSX I get the error message Spreadsheet couldn't be imported. An error occurred when I tried to open in IOS. This as the first time I edited in OSX since the iPhone was upgraded to IOS7.

I have edited the spreadsheet down so that it is just a simple table - to make sure that my recent edits had not caused an incompatibility.

I have looked at the problem spreadsheet in iCloud and it seems OK.
I also got a backup via Time Machine on OSX of before I opened it in OSX and that is openable in IOS

The errors Occur with Numbers '09 2.3(554) on OSX 10.8.5 and Numbers on IOS 7.0.2 

How can I find out what is causing the error (and then fix it)
I had the same problem.
A hard reset of my iPad (press and hold both the home button and the power button until the device turns off, then wait while it reboots) solved the issue.