Synchronise failure.

Lots of new contacts added but every one comes up with an error although the new contacts still appear in eMClient. However, they are not synchornising with my Google accound so are not appearing on my Android phone.
13:28:43    at MailClient.Commands.Command.Process(WorkerStatus status)
13:29:36   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:29:36    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:29:36    at MailClient.Commands.Command.Process(WorkerStatus status)
13:29:53   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:29:53    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:29:53    at MailClient.Commands.Command.Process(WorkerStatus status)
13:30:01   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:30:01    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:30:01    at MailClient.Commands.Command.Process(WorkerStatus status)
13:30:51   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:30:51    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:30:51    at MailClient.Commands.Command.Process(WorkerStatus status)
13:33:32   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:33:32    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:33:32    at MailClient.Commands.Command.Process(WorkerStatus status)
13:34:24   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:34:24    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:34:24    at MailClient.Commands.Command.Process(WorkerStatus status)
13:45:26 [email protected] [Google Contacts]  Synchronizing folder list
13:45:26 [email protected] [Google Contacts]  Synchronizing folder list
13:45:26 [email protected] [Google Contacts]  Uploading item(s) to folder ‘[email protected]/Contacts/’
13:45:26   MailClient.Storage.Application.OperationException: Uploading item(s) to folder ‘[email protected]/Contacts/’ failed due to the following error: Execution of request failed: https://www.google.com/m8/feeds/contacts/default/full (Invalid request.)
13:45:26    at MailClient.Protocols.Gdata.GenericGdataCommand.Execute(WorkerStatus status)
13:45:26    at MailClient.Commands.Command.Process(WorkerStatus status)

Copy your contacts to Local Folders. If Local Folders are not visible you can enable them in Menu > Tools > Settings > General > Show Local Folders.

Once the contacts are copied, go to Menu > Tools > Accounts and remove the Gmail account. Then add it again. Once it has synced, copy the missing contacts from Local Folders to the Gmail contact folder.

I cannot copy the Contacts back to the main account folder. The error message says “Folder has been deleted”.
My main account is NOT a Gmail account but an IMAP account on my own ISP server.

Well, an IMAP account itself does not provide contact syncing. It would need to have  a service like CardDAV or something similar.

Who is your email provider for that account?