Error 500

Hi,

i am getting this error frequently:

Error 500: Internal Server Error, Kindly reopen the file and try again.

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This error occurs suddenly and at times when i save the sheet.

THis error is not occuring on docs.

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System Config: Used IE7.1, Netscape 9.2, Win XP SP2

error occurs in many systems. the error repeats every 15 secs.

Kindly correct or indicate what is the cause of the error. if this is not rectifiable, then it will be of no use for us in using zoho sheets.
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another error / feedback: the system is very slow to upload / refresh. many a time, it is very difficult to keep track of changes that is done. the server's response time is pathetic.

thanks and regards
mukundan
mukundanraghavan