OLMAPI32.dll is an Outlook file and required for the smooth running of Outlook. The above issue occurs when you install new program in your PC or due to corrupt Outlook files. To solve this issue follow below methods:
1. Remove any newly installed software and check if error is still occurring.
2. Above issue also occurs if your PC is infected with virus. So scan your PC with antivirus software and remove the virus.
3. Rename OLMAPI32.dll. First close Outlook, now go to location C:\Program Files\Microsoft Office\Office14 and locate OLMAPI32.DLL (For Outlook 2010). Rename it with OLMAPI32.old. Repair Office 2010.