Hi Ritanand,
I remember a colleague having a similar issue in the past. She had a file that would be read sometimes and othertimes she was getting the same error. The sheet name was also 31 characters to match the limit in for an Excel sheet name and contained no special characters.
She noticed that when the sheetname was 'Sheet1', it always worked. So she shortened the sheet name down from 31 characters to 30 or less. Whatever applications were being used read the sheet name string in a weird way, and would add an underscore to the end making the sheet name 32 characters when it is read.
Maybe someone else has experienced the issue directly and will know the proper solution.
Kind regards,
Ben